Systems and methods for electrosurgical prevention of disc herniations

ABSTRACT

The present invention provides systems and methods for selectively applying electrical energy to a target location within a patient&#39;s body, particularly including tissue in the spine. The present invention applies high frequency (RF) electrical energy to one or more electrode terminals in the presence of electrically conductive fluid or saline-rich tissue to contract collagen fibers within the tissue structures. In one aspect of the invention, a system and method is provided for contracting a portion of the nucleus pulposus of a vertebral disc by applying a high frequency voltage between an active electrode and a return electrode within the portion of the nucleus pulposus, where contraction of the portion of nucleus pulposus inhibits migration of the portion nucleus pulposus through the fissure.

RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 09/026,698 filed Feb. 20, 1998 which is acontinuation-in-part of U.S. Pat. No. 5,902,272, the complete disclosureof each which are incorporated herein by reference for all purposes.

[0002] The present invention is related to commonly assigned co-pendingProvisional Patent Application Nos. 60/062,996 and 60/062,997,non-provisional U.S. patent application Ser. No. 08/970,239 entitled“Electrosurgical Systems and Methods for Treating the Spine”, filed Nov.14, 1997 (Attorney Docket No. 16238-001640), and Ser. No. 08/977,845entitled “Systems and Methods for Electrosurgical DermatologicalTreatment”, filed on Nov. 25, 1997 (Attorney Docket No. D-2), U.S.application Ser. No. 08/753,227, filed on Nov. 22, 1996 (Docket16238-002200), and PCT International Application, U.S. National PhaseSerial No. PCT/US94/05168, filed on May 10, 1994, now U.S. Pat. No.5,697,281, (Attorney Docket 16238000440), which was acontinuation-in-part of application Ser. No. 08/059,681, filed on May10, 1993 (Attorney Docket 16238-000420), which was acontinuation-in-part of application Ser. No. 07/958,977, filed on Oct.9, 1992 (Attorney Docket 16238-000410) which was a continuation-in-partof application Ser. No. 07/817,575, filed on Jan. 7, 1992 (AttorneyDocket 16238-00040), the complete disclosures of which are incorporatedherein by reference for all purposes. The present invention is alsorelated to commonly assigned U.S. Pat. No. 5,683,366, filed Nov. 22,1995 (Attorney Docket 16238-000700), and U.S. Pat. No. 5,697,536, filedon Jun. 2, 1995 (Attorney Docket 16238-0006000), the completedisclosures of which are incorporated herein by reference for allpurposes.

BACKGROUND OF THE INVENTION

[0003] The present invention relates to the field of electrosurgery, andmore particularly to surgical devices and methods which employhigh-frequency electrical energy to treat soft tissue in regions of thespine. The present invention also relates to improved devices andmethods for the treatment of intervertebral discs

[0004] Intervertebral discs mainly function to articulate and cushionthe vertebrae, while the interspinous tissue (i.e., tendons andcartilage, and the like) function to support the vertebrae so as toprovide flexibility and stability to the patient's spine.

[0005] The discs comprise a nucleus pulposus which is a centralhydrophilic cushion. The nucleus is surrounded by an annulus fibrosus orannulus which is a multi-layered fibrous ligament. The disc alsoincludes vertebral endplates which are located between the disc andadjacent vertebrae.

[0006] The nucleus pulposus occupies 25-40% of the total disccross-sectional area. It is composed mainly of mucoid materialcontaining mainly proteoglycans with a small amount of collagen. Theproteoglycans consist of a protein core having attached chains ofnegatively charged keratin sulphate and chondroitin sulphate. Such astructure is the reason the nucleus pulposus is a “loose or amorphoushydrogel” which has the capacity to bind water and usually contains70-90% water by weight.

[0007] The annulus fibrosus forms the outer boundary of the disc and iscomposed of highly structured collagen fibers embedded in amorphous basesubstance also composed of water and proteoglycans. However, theamorphous base of the annulus is lower in content than in the nucleus.The collagen fibers of the annulus are arranged in concentric laminatedbands. In each laminated band the fibers are parallel and attached tothe adjacent vertebral bodies at roughly a 30° angle from the horizontalplane of the disc in both directions. There is a steady increase in theproportion of collagen from the inner to the outer annulus.

[0008] Each disc has two vertebral end-plates composed of hyalinecartilage. As mentioned above, the end-plates separate the disc fromadjacent vertebral bodies. The end-plates acts as a transitional zonebetween the harder bony vertebral bodies and the soft disc. Because thenucleus pulposus does not contain blood vessels (i.e., it is avascular),the disc receives most nutrients through the end-plate areas.

[0009] Many patients suffer from discogenic pain resulting fromdegenerative disc disease and/or vertebral disc herniation. Degenerationof discs occurs when they lose their water content and height, causingadjoining vertebrae to move closer together. The deterioration of thedisc results in a decrease of the shock-absorbing ability of the spine.This condition also causes a narrowing of the neural openings in thesides of the spine which may pinch these nerves. Thus disc degenerationmay eventually cause severe chronic and disabeling back and leg pain.

[0010] Disc herniations generally fall into three types ofcategories: 1) contained disc herniation (also known as contained discprotrusion); 2) extruded disc herniation; and 3) sequestered discherniation (also known as a free fragment.)

[0011] In a contained herniation, a portion of the disc protrudes orbulges from a normal boundary of the disc. However, in a containedherniation, the nucleus pulposus and the disc do not breach the annulusfibrosus, rather a protrusion of the disc might mechanically compressand/or chemically irritate an adjacent nerve root. This condition leadsto radicular pain, commonly referred to as sciatica (leg pain.) In anextruded herniation, the annulus is disrupted and a segment of thenucleus protrudes/extrudes from the disc. However in this condition, thenucleus within the disc remains contiguous with the extruded fragment.With a sequestered disc herniation, a nucleus fragment separates fromthe nucleus and disc.

[0012] Degenerating or injured discs may have weaknesses in the annuluscontributing to herniation of the disc. The weakened annulus may allowfragments of nucleus pulposus to migrate through the annulus fibrosusand into the spinal canal. Once in the canal, the displaced nucleuspulposus tissue, or the protruding annulus may impinge on spinal nervesor nerve roots. A weakened annulus may also result in bulging (e.g., acontained herniation) of the disc. Mechanical compression and/orchemical irritation of the nerve may occur depending on the proximity ofthe bulge to a nerve. A patient with these conditions may experiencepain, sensory, and motor deficit.

[0013] A significant percentage of such patients undergo surgicalprocedures to treat the disorders described above. These proceduresinclude both percutaneous and open discectomy, and spinal fusion.

[0014] Often, symptoms from disc herniation can be treated successfullyby non-surgical means, such as rest, therapeutic exercise, oralanti-inflammatory medications or epidural injection of corticosteroids.Such treatments result in a gradual but progressive improvement insymptoms and allow the patient to avoid surgical intervention.

[0015] In some cases, the disc tissue is irreparably damaged, therebynecessitating removal of a portion of the disc or the entire disc toeliminate the source of inflammation and pressure. In more severe cases,the adjacent vertebral bodies must be stabilized following excision ofthe disc material to avoid recurrence of the disabling back pain. Oneapproach to stabilizing the vertebrae, termed spinal fusion, is toinsert an interbody graft or implant into the space vacated by thedegenerative disc. In this procedure, a small amount of bone may begrafted and packed into the implants. This allows the bone to growthrough and around the implant, fusing the vertebral bodies andpreventing reoccurrence of the symptoms.

[0016] Until recently, surgical spinal procedures resulted in majoroperations and traumatic dissection of muscle and bone removal or bonefusion. However, the development of minimally invasive spine surgeryovercomes many of the disadvantages of traditional traumatic spinesurgery. In endoscopic spinal procedures, the spinal canal is notviolated and therefore epidural bleeding with ensuing scarring isminimized or completely avoided. In addition, the risk of instabilityfrom ligament and bone removal is generally lower in endoscopicprocedures than with open procedures. Further, more rapid rehabilitationfacilitates faster recovery and return to work.

[0017] Percutaneous techniques for the treatment of herniated discsinclude: chemonucleolysis; laser techniques; mechanical techniques, suchas automated percutaneous lumbar discectomy; and Nucleoplasty usingCoblation plasma technology. These procedures generally require thesurgeon to place an introducer needle or cannula from the externalsurface of the patient to the spinal disc(s) for passage of surgicalinstruments or device. Open techniques for the treatment of herniateddiscs involve surgical dissection through soft tissue and removal of aportion of vertebral bone. Conventionally, upon encountering the annulusa complex surgical incision, called an annulotomy, must be made to allowaccess of instruments into the disc so that decompress the disc may takeplace. Mechanical instruments, such as pituitary rongeurs, curettes,graspers, cutters, drills, microdebriders and the like are often used toremove the nucleus material. Unfortunately, these mechanical instrumentsgreatly lengthen and increase the complexity of the procedure. Inaddition, and most significantly, the annulotomy itself may lead tofuture re-herniation of the disc or even accelerate disc degeneration.Discussion of the problems associated with the annulotomy are found injournals and other medical publications. (see e.g., Ahlgren, et al.Annular incision technique on the strength and multidirectionalflexibility of the healing intervertebral disc., Spine, Apr. 15, 1994;9(8) pp 948-954; Ahlgren, et al. Effect of annular repair on the healingstrength of the intervertebral disc: a sheep model., Spine, Sep. 1,2000; 25(17): pp 2167-2170.)

[0018] Previously, in order to reduce the risk of re-herniation of theannulus subsequent to the performance of an annulotomy, the surgeonremoves an excess amount of nucleus material from the disc than thatrequired to normally decompress the disc. However, it was found thatremoving an excess amount of the nucleus pulposus destabilizes the discleading to accelerated disc degeneration. See e.g., Meakin et al., TheEffect of Partial Removal of the Nucleus Pulposus from theIntervertebral Disc on the Response of the Human Annulus Fibrosus toCompression., Clin Biomech (Bristol, Avon) Feb. 16, 2001 (2) pp.121-128.

[0019] Monopolar and bipolar radiofrequency devices have been used inlimited roles in spine surgery, primarily for hemostasis. Monopolardevices, however, suffer from the disadvantage that the electric currentwill flow through undefined paths in the patient's body, therebyincreasing the risk of undesirable electrical stimulation to portions ofthe patient's body. In addition, since the defined path through thepatient's body has a relatively high impedance (because of the largedistance or resistivity of the patient's body), large voltagedifferences must typically be applied between the return and activeelectrodes in order to generate a current suitable for ablation orcutting of the target tissue. This current, however, may inadvertentlyflow along body paths having less impedance than the defined electricalpath, which will substantially increase the current flowing throughthese paths, possibly causing damage to or destroying surrounding tissueor neighboring peripheral nerves.

[0020] Another significant disadvantage of conventional RF devices,particularly monopolar devices, is that the device causes nervestimulation and interference with nerve monitoring equipment in theoperating room. In addition, these devices typically operate by creatinga voltage difference between the active electrode and the target tissue,causing an electrical arc to form across the physical gap between theelectrode and tissue. At the point of contact of the electric arcs withtissue, rapid tissue heating occurs due to high current density betweenthe electrode and tissue. This high current density increases thetemperature of the cells causing cellular fluids to rapidly vaporizeinto steam, thereby producing a “cutting effect” by exploding the cellsalong the pathway of localized tissue heating. Thus, while the tissueparts along the pathway of evaporated cellular fluid, the heatingprocess induces undesirable thermal collateral tissue damage in regionssurrounding the target tissue site. This collateral tissue damage oftenincludes indiscriminate destruction of tissue, resulting in thermalnecrosis and the loss of the proper function of the tissue. In addition,the conventional device does not remove any tissue directly, but ratherdepends on destroying a zone of tissue and allowing the body to eitherencapsulate the zone with scar tissue or eventually remove the destroyedtissue via phagocytosis absorption.

[0021] A further problem with lasers and conventional RF devices is thatthe conduction of heat may cause unintentional damage to the vertebralend-plates. The vertebral end-plates contain chondrocytes which extractplasma and other nutrients from adjacent micro-capillaries to maintainthe essential moisture and biochemistry within the disc. However, thesechondrocytes are heat sensitive. Therefore, thermally damaging thesechondrocytes may also destroy or impair the function of the vertebralend-plates thereby causing premature disc deterioration. In addition,damage of the end-plates may cause the adjacent formation of necrotictissue, and/or thermal bone necrosis (i.e., a layer of dead bone),thereby creating a barrier to the passage of water and nutrients fromthe endplate into the disc. Such a condition may further accelerate thedegeneration of the disc. The existence of necrotic tissue may alsopresent problems if a fusion procedure is subsequently required. Anynecrotic tissue at the site of the area to be fused must be removed ordestroyed prior to fusion. Accordingly, the presence of necrotic tissueincreases the duration of the fusion procedure and may adversely affectthe outcome of the procedure.

[0022] Presently, there is a need for an improved treatment forindividuals having disorders or abnormalities of an intervertebral disc.There is also a need to prevent disc herniations, especially extrudeddisc herniations and sequestered disc herniation (free fragments) whenthe annulus of the disc is weakened and/or diseased.

[0023] The methods and devices aimed at meeting the above needs shouldbe applicable to all types of degenerative discs, and all levels of thevertebral column, including cervical, thoracic, and lumbar spine. Suchmethods and devices should also be applicable to all types ofherniations.

SUMMARY OF THE INVENTION

[0024] The present invention provides systems, apparatus and methods forselectively applying electrical energy to structures within a patient'sbody, such as tissue within or around the spine. The systems and methodsof the present invention are particularly useful for ablation,resection, aspiration, collagen shrinkage and/or hemostasis of tissueand other body structures in spine surgery.

[0025] The invention includes a method for inhibiting herniation and/orreherniation of a vertebral disc, the vertebral disc including anannulus, a nucleus pulposus, and at least one fissure in the annulus,the method comprising positioning a distal end of a shaft of anelectrosurgical probe into the disc, the probe having a plurality ofelectrodes coupled to a high frequency power supply, the plurality ofelectrodes comprising at least one active electrode and at least onereturn electrode, the active electrodes being disposed towards thedistal end of the shaft, positioning at least one active electrodewithin a portion of the nucleus pulposus, the portion being adjacent toand/or in contact with the fissure, and contracting the portion ofnucleus pulposus by applying a high frequency voltage between the atleast one active electrode and the at least one return electrode withinthe portion of the nucleus pulposus, where contraction of the portion ofnucleus pulposus inhibits migration of the portion nucleus pulposusthrough the fissure.

[0026] A variation of the above described method further includescoagulating nucleus pulposus fragments and fissures to “seal” thenucleus and inhibit future fragments and herniations.

[0027] A variation of the above described method further includesablating or vaporizing the nucleus pulposus. Where ablating orvaporizing the nucleus pulposus may occur prior to, subsequent to, orcontemporaneous to the act of contracting the portion of nucleuspulposus.

[0028] The act of ablating/vaporizing the nucleus pulposus may occurwith a second electrosurgical probe, where the first electrosurgicalprobe is not adapted to ablate and/or vaporize tissue.

[0029] The inventive method may further include wherein inserting animplant material between the contracted portion of the nucleus pulposusand the fissure. The implant material may be a sealant selected from agroup consisting of a metal, ceramic, polyurethane, hydrogel, proteinhydrogel, thermopolymer, adhesive, collagen, and fibrogen glue.

[0030] The inventive method may be performed via an open surgery or viaa percutaneous incision in a minimally invasive manner. The percutaneouspenetration may be located on the patient's back, abdomen, or thorax.Alternatively, the method may be performed by introducing theelectrosurgical probe anteriorly through the patient to the spine.

[0031] In procedures requiring contraction of tissue, high frequencyvoltage is applied to the electrode terminal(s) to elevate thetemperature of collagen fibers within the tissue at the target site frombody temperature (about 37° C.) to a tissue temperature in the range ofabout 45° C. to 90° C., usually about 60° C. to 70° C., to substantiallyirreversibly contract these collagen fibers. In a preferred embodiment,an electrically conducting fluid is provided between the electrodeterminal(s) and one or more return electrode(s) positioned proximal tothe electrode terminal(s) to provide a current flow path from theelectrode terminal(s) away from the tissue to the return electrode (s).The current flow path may be generated by directing an electricallyconducting fluid along a fluid path past the return electrode and to thetarget site, or by locating a viscous electrically conducting fluid,such as a gel, at the target site, and submersing the electrodeterminal(s) and the return electrode(s) within the conductive gel. Thecollagen fibers may be heated either by passing the electric currentthrough the tissue to a selected depth before the current returns to thereturn electrode(s) and/or by heating the electrically conducting fluidand generating a jet or plume of heated fluid, which is directed towardsthe target tissue. In the latter embodiment, the electric current maynot pass into the tissue at all. In both embodiments, the heated fluidand/or the electric current elevates the temperature of the collagensufficiently to cause hydrothermal shrinkage of the collagen fibers.

[0032] In procedures requiring ablation of tissue, the tissue is removedby molecular dissociation or disintegration processes. In theseembodiments, the high frequency voltage applied to the electrodeterminal(s) is sufficient to vaporize an electrically conductive fluid(e.g., gel or saline) between the electrode terminal(s) and the tissue.Within the vaporized fluid, a ionized plasma is formed and chargedparticles (e.g., electrons) are accelerated towards the tissue to causethe molecular breakdown or disintegration of several cell layers of thetissue. This molecular dissociation is accompanied by the volumetricremoval of the tissue. The short range of the accelerated chargedparticles within the plasma layer confines the molecular dissociationprocess to the surface layer to minimize damage and necrosis to theunderlying tissue. This process can be precisely controlled to effectthe volumetric removal of tissue as thin as 10 to 150 microns withminimal heating of, or damage to, surrounding or underlying tissuestructures. A more complete description of this phenomena is describedin commonly assigned U.S. Pat. No. 5,683,366, the complete disclosure ofwhich is incorporated herein by reference.

[0033] In another aspect of the invention, the present invention isuseful for helping to create an operating corridor or passage between apercutaneous penetration in the patient's outer skin and a target areawithin the spine. Typically, this operating corridor is initiallycreated by inserting one or more dilators through the percutaneouspenetration to the target area within the spine, and then introducing atubular retractor or similar instrument over the largest dilator. Oncethis is accomplished, the hollow interior of the retractor (which willserve as the operating corridor for the introduction of the necessaryinstruments, such as the endoscope) is typically partially filled withsoft tissue, muscle and other body structures. The present invention isparticularly useful for precisely and quickly removing these bodystructures to clear the operating corridor. To that end, anelectrosurgical probe according to the invention is delivered into thehollow retractor, and one or more electrode terminal(s) are positionedadjacent to or in contact with the soft tissue or other body structuresto be removed. High frequency voltage is applied between the electrodeterminal(s) and one or more return electrodes such that the tissue isremoved.

[0034] The tissue may be completely ablated in situ with the mechanismsdescribed above, or the tissue may be partially ablated and partiallyresected and aspirated from this operating corridor. In the latterembodiment, the method of the present invention further comprisesaspirating tissue fragments and fluid through an aspiration lumen in theelectrosurgical instrument or another instrument. In a preferredconfiguration, the probe will include one or more aspirationelectrode(s) at or near the distal opening of the aspiration lumen. Inthis embodiment, high frequency voltage is applied between theaspiration electrode(s) and one or more return electrode(s) (which canbe the same or different electrodes from the ones used to ablate tissue)to partially or completely ablate the tissue fragments as they areaspirated into the lumen, thus inhibiting clogging of the lumen andexpediting the tissue removal process.

[0035] The present invention offers a number of advantages over currentmechanical and laser techniques for spine surgery. The ability toprecisely control the volumetric removal of tissue results in a field oftissue ablation or removal that is very defined, consistent andpredictable. The shallow depth of tissue heating also helps to minimizeor completely eliminate damage to healthy tissue structures, cartilage,bone and/or spinal nerves that are often adjacent the target tissue. Inaddition, small blood vessels within the tissue are simultaneouslycauterized and sealed as the tissue is removed to continuously maintainhemostasis during the procedure. This increases the surgeon's field ofview, and shortens the length of the procedure. Moreover, since thepresent invention allows for the use of electrically conductive fluid(contrary to prior art bipolar and monopolar electrosurgery techniques),isotonic saline may be used during the procedure. Saline is thepreferred medium for irrigation because it has the same concentration asthe body's fluids and, therefore, is not absorbed into the body as muchas other fluids. Alternatively, saline-rich tissue can be used as theconductive medium.

[0036] Apparatus according to the present invention generally include anelectrosurgical probe or catheter having a shaft with proximal anddistal ends, one or more electrode terminal(s) at the distal end and oneor more connectors coupling the electrode terminal(s) to a source ofhigh frequency electrical energy. The shaft will have a distal endportion sized to fit between adjacent vertebrae in the patient's spine.In some embodiments, the distal end portion is substantially planar, andit offers a low profile, to allow access to confined spaces withoutrisking iatrogenic injury to surrounding body structures or nerves, suchas vertebrae or spinal nerves. Usually, the distal end portion will havea combined height (i.e., including the active electrode(s)) of less than2 mm and preferably less than 1 mm.

[0037] The apparatus will preferably further include a fluid deliveryelement for delivering electrically conducting fluid to the electrodeterminal(s) and the target site. The fluid delivery element may belocated on the probe, e.g., a fluid lumen or tube, or it may be part ofa separate instrument. Alternatively, an electrically conducting gel orspray, such as a saline electrolyte or other conductive gel, may beapplied the target site, or saline-rich tissue may be used, such as thenucleus. In this embodiment, the apparatus may not have a fluid deliveryelement. In both embodiments, the electrically conducting fluid willpreferably generate a current flow path between the electrodeterminal(s) and one or more return electrode(s). In an exemplaryembodiment, the return electrode is located on the probe and spaced asufficient distance from the electrode terminal(s) to substantiallyavoid or minimize current shorting therebetween and to shield the returnelectrode from tissue at the target site.

[0038] In a specific configuration, the electrosurgical probe willinclude an electrically insulating electrode support member having atissue treatment surface at the distal end of the probe. One or moreelectrode terminal(s) are coupled to, or integral with, the electrodesupport member such that the electrode terminal(s) are spaced from thereturn electrode. In one embodiment, the probe includes an electrodearray having a plurality of electrically isolated electrode terminalsembedded into the electrode support member such that the electrodeterminals extend about 0.2 mm to about 10 mm distally from the tissuetreatment surface of the electrode support member. In this embodiment,the probe will further include one or more lumens for deliveringelectrically conductive fluid to one or more openings around the tissuetreatment surface of the electrode support member. In an exemplaryembodiment, the lumen will extend through a fluid tube exterior to theprobe shaft that ends proximal to the return electrode.

[0039] The system may optionally include a temperature controllercoupled to one or more temperature sensors at or near the distal end ofthe probe. The controller adjusts the output voltage of the power supplyin response to a temperature set point and the measured temperaturevalue. The temperature sensor may be, for example, a thermocouple,located in the insulating support that measures a temperature at thedistal end of the probe. In this embodiment, the temperature set pointwill preferably be one that corresponds to a tissue temperature thatresults, for example, in the contraction of the collagen tissue, i.e.,about 60° C. to 70° C. Alternatively, the temperature sensor maydirectly measure the tissue temperature (e.g., infrared sensor).

BRIEF DESCRIPTION OF THE DRAWINGS

[0040]FIG. 1 is a perspective view of an electrosurgical systemincorporating a power supply and an electrosurgical probe for tissueablation, resection, incision, contraction and for vessel hemostasisaccording to the present invention;

[0041]FIG. 2 is a side view of an electrosurgical probe according to thepresent invention;

[0042]FIG. 3 is a cross-sectional view of a distal portion of the probeof FIG. 2;

[0043]FIG. 4 is an end view of the probe of FIG. 2, illustrating anarray of active electrode terminals;

[0044]FIG. 5 is an exploded view of the electrical connections withinthe probe of FIG. 2;

[0045] FIGS. 6-10 are end views of alternative embodiments of the probeof FIG. 2, incorporating aspiration electrode(s);

[0046] FIGS. 11A-11C illustrate an alternative embodiment incorporatinga mesh electrode for ablating aspirated tissue fragments;

[0047] FIGS. 12-15 illustrate a method of performing a microendoscopicdiscectomy according to the principles of the present invention;

[0048]FIG. 16 is a schematic view of the proximal portion of anotherelectrosurgical system for endoscopic spine surgery incorporating anelectrosurgical instrument according to the present invention;

[0049]FIG. 17 is an enlarged view of a distal portion of theelectrosurgical instrument of FIG. 16;

[0050]FIG. 18 illustrates a method of ablating a volume of tissue fromthe nucleus pulposis of a herniated disc with the electrosurgical systemof FIG. 16;

[0051]FIG. 19 illustrates a planar ablation probe for ablating tissue inconfined spaces within a patient's body according to the presentinvention;

[0052]FIG. 20 illustrates a distal portion of the planar ablation probeof FIG. 19;

[0053]FIG. 21A is a front sectional view of the planar ablation probe,illustrating an array of semi-cylindrical active electrodes;

[0054]FIG. 21B is a front sectional view of an alternative planarablation probe, illustrating an array of active electrodes havingopposite polarities;

[0055]FIG. 22 is a top, partial section, view of the working end of theplanar ablation probe of FIG. 19;

[0056]FIG. 23 is a side cross-sectional view of the working end of theplanar ablation probe, illustrating the electrical connection with oneof the active electrodes of FIG. 22;

[0057]FIG. 24 is a side cross-sectional view of the proximal end of theplanar ablation probe, illustrating the electrical connection with apower source connector;

[0058]FIG. 25 is a schematic view illustrating the ablation of meniscustissue located close to articular cartilage between the tibia and femurof a patient with the ablation probe of FIG. 19;

[0059]FIG. 26 is an enlarged view of the distal portion of the planarablation probe, illustrating ablation or cutting of meniscus tissue;

[0060]FIG. 27 illustrates a method of ablating tissue with a planarablation probe incorporating a single active electrode;

[0061]FIG. 28 is a schematic view illustrating the ablation of softtissue from adjacent surfaces of the vertebrae with the planar ablationprobe of the present invention;

[0062]FIG. 29 is a perspective view of an alternative embodiment of theplanar ablation probe incorporating a ceramic support structure withconductive strips printed thereon;

[0063]FIG. 30 is a top partial cross-sectional view of the planarablation probe of FIG. 29;

[0064]FIG. 31 is an end view of the probe of FIG. 30;

[0065]FIGS. 32A and 32B illustrate an alternative cage aspirationelectrode for use with the electrosurgical probes shown in FIGS. 2-11;

[0066] FIGS. 33A-33C illustrate an alternative dome shaped aspirationelectrode for use with the electrosurgical probes of FIGS. 2-11;

[0067] FIGS. 34-36 illustrates another system and method of the presentinvention for percutaneously contracting collagen fibers within a spinaldisc with a small, needle-sized instrument;

[0068]FIG. 37 is a variation of an exemplary surgical system for usewith the present invention;

[0069] FIGS. 38-41 illustrate variations of electrosurgical probes ofthe present invention;

[0070] FIGS. 42-50 show examples of a working end of variations ofprobes of the present invention;

[0071]FIG. 51 illustrates a vertebral disc having a portion of a nucleuspulposus prone to extrude through an annulus resulting in a herniationor re-herniation of the disc;

[0072]FIG. 52 illustrates a method of heating a portion of a nucleuspulposus prone to minimize the potential of a herniation orre-herniation of the disc; and

[0073]FIG. 53 illustrates inserting a material into the vertebral discto further prevent the occurrence of disc herniation.

DESCRIPTION OF SPECIFIC EMBODIMENTS

[0074] The present invention provides systems and methods forselectively applying electrical energy to a target location within or ona patient's body, particularly including tissue or other body structuresin the spine. These procedures include laminectomy/disketomy proceduresfor treating herniated disks, decompressive laminectomy for stenosis inthe lumbosacral and cervical spine, medial facetectomy, posteriorlumbosacral and cervical spine fusions, treatment of scoliosisassociated with vertebral disease, foraminotomies to remove the roof ofthe intervertebral foramina to relieve nerve root compression andanterior cervical and lumbar diskectomies. These procedures may beperformed through open procedures, or using minimally invasivetechniques, such as thoracoscopy, arthroscopy, laparascopy or the like.

[0075] In the present invention, high frequency (RF) electrical energyis applied to one or more electrode terminals in the presence ofelectrically conductive fluid to remove and/or modify the structure oftissue structures. Depending on the specific procedure, the presentinvention may be used to: (1) volumetrically remove tissue, bone,ligament or cartilage (i.e., ablate or effect molecular dissociation ofthe body structure); (2) cut or resect tissue or other body structures;(3) shrink or contract collagen connective tissue; and/or (4) coagulatesevered blood vessels.

[0076] In some procedures, e.g., shrinkage of nucleus pulposis inherniated discs, it is desired to shrink or contract collagen connectivetissue at the target site. In these procedures, the RF energy heats thetissue directly by virtue of the electrical current flow therethrough,and/or indirectly through the exposure of the tissue to fluid heated byRF energy, to elevate the tissue temperature from normal bodytemperatures (e.g., 37° C.) to temperatures in the range of 45° C. to90° C., preferably in the range from about 60° C. to 70° C. Thermalshrinkage of collagen fibers occurs within a small temperature rangewhich, for mammalian collagen is in the range from 60° C. to 70° C.(Deak, G., et al., “The Thermal Shrinkage Process of Collagen Fibres asRevealed by Polarization Optical Analysis of Topooptical StainingReactions,” Acta Morphologica Acad. Sci. of Hungary, Vol. 15(2), pp195-208, 1967). Collagen fibers typically undergo thermal shrinkage inthe range of 60° C. to about 70° C. Previously reported research hasattributed thermal shrinkage of collagen to the cleaving of the internalstabilizing cross-linkages within the collagen matrix (Deak, ibid). Ithas also been reported that when the collagen temperature is increasedabove 70° C., the collagen matrix begins to relax again and theshrinkage effect is reversed resulting in no net shrinkage (Allain, J.C., et al., “Isometric Tensions Developed During the HydrothermalSwelling of Rat Skin,” Connective Tissue Research, Vol. 7, pp 127-133,1980). Consequently, the controlled heating of tissue to a precise depthis critical to the achievement of therapeutic collagen shrinkage. A moredetailed description of collagen shrinkage can be found in U.S. patentapplication Ser. No. 08/942,580, filed Oct. 2, 1997, entitled “SYSTEMSAND METHODS FOR ELECTROSURGICAL TISSUE CONTRACTION” (Attorney Docket No.16238-001300), previously incorporated herein by reference.

[0077] The preferred depth of heating to effect the shrinkage ofcollagen in the heated region (i.e., the depth to which the tissue iselevated to temperatures between 60° C. to 70° C.) generally depends on(1) the thickness of the tissue, (2) the location of nearby structures(e.g., nerves) that should not be exposed to damaging temperatures,and/or (3) the volume of contraction desired to relieve pressure on thespinal nerve. The depth of heating is usually in the range from 0 to 3.5mm. In the case of collagen within the nucleus pulposis, the depth ofheating is preferably in the range from about 0 to about 2.0 mm.

[0078] In another method of the present invention, the tissue structuresare volumetrically removed or ablated. In this procedure, a highfrequency voltage difference is applied between one or more electrodeterminal(s) and one or more return electrode(s) to develop high electricfield intensities in the vicinity of the target tissue site. The highelectric field intensities lead to electric field induced molecularbreakdown of target tissue through molecular dissociation (rather thanthermal evaporation or carbonization). Applicant believes that thetissue structure is volumetrically removed through moleculardisintegration of larger organic molecules into smaller molecules and/oratoms, such as hydrogen, oxides of carbon, hydrocarbons and nitrogencompounds. This molecular disintegration completely removes the tissuestructure, as opposed to dehydrating the tissue material by the removalof liquid within the cells of the tissue, as is typically the case withelectrosurgical desiccation and vaporization.

[0079] The high electric field intensities may be generated by applyinga high frequency voltage that is sufficient to vaporize an electricallyconducting fluid over at least a portion of the electrode terminal(s) inthe region between the distal tip of the electrode terminal(s) and thetarget tissue. The electrically conductive fluid may be a gas or liquid,such as isotonic saline, delivered to the target site, or a viscousfluid, such as a gel, that is located at the target site, or saline-richtissue such as the nucleus pulposus. In the latter embodiments, theelectrode terminal(s) are submersed in the electrically conductive gelduring the surgical procedure. Since the vapor layer or vaporized regionhas a relatively high electrical impedance, it increases the voltagedifferential between the electrode terminal tip and the tissue andcauses ionization within the vapor layer due to the presence of anionizable species (e.g., sodium when isotonic saline is the electricallyconducting fluid). This ionization, under optimal conditions, inducesthe discharge of energetic electrons and photons from the vapor layerand to the surface of the target tissue. This energy may be in the formof energetic photons (e.g., ultraviolet radiation), energetic particles(e.g., electrons) or a combination thereof. A more detailed descriptionof this cold ablation phenomena, termed Coblation™, can be found incommonly assigned U.S. Pat. No. 5,683,366 the complete disclosure ofwhich is incorporated herein by reference.

[0080] The present invention applies high frequency (RF) electricalenergy in an electrically conducting fluid environment to remove (i.e.,resect, cut or ablate) or contract a tissue structure, and to sealtransected vessels within the region of the target tissue. The presentinvention is particularly useful for sealing larger arterial vessels,e.g., on the order of 1 mm or greater. In some embodiments, a highfrequency power supply is provided having an ablation mode, wherein afirst voltage is applied to an electrode terminal sufficient to effectmolecular dissociation or disintegration of the tissue, and acoagulation mode, wherein a second, lower voltage is applied to anelectrode terminal (either the same or a different electrode) sufficientto achieve hemostasis of severed vessels within the tissue. In otherembodiments, an electrosurgical probe is provided having one or morecoagulation electrode(s) configured for sealing a severed vessel, suchas an arterial vessel, and one or more electrode terminals configuredfor either contracting the collagen fibers within the tissue or removing(ablating) the tissue, e.g., by applying sufficient energy to the tissueto effect molecular dissociation. In the latter embodiments, thecoagulation electrode(s) may be configured such that a single voltagecan be applied to coagulate with the coagulation electrode(s), and toablate or contract with the electrode terminal(s). In other embodiments,the power supply is combined with the coagulation probe such that thecoagulation electrode is used when the power supply is in thecoagulation mode (low voltage), and the electrode terminal(s) are usedwhen the power supply is in the ablation mode (higher voltage).

[0081] In the method of the present invention, one or more electrodeterminals are brought into close proximity to tissue at a target site,and the power supply is activated in the ablation mode such thatsufficient voltage is applied between the electrode terminals and thereturn electrode to volumetrically remove the tissue through moleculardissociation, as described below. During this process, vessels withinthe tissue will be severed. Smaller vessels will be automatically sealedwith the system and method of the present invention. Larger vessels, andthose with a higher flow rate, such as arterial vessels, may not beautomatically sealed in the ablation mode. In these cases, the severedvessels may be sealed by activating a control (e.g., a foot pedal) toreduce the voltage of the power supply into the coagulation mode. Inthis mode, the electrode terminals may be pressed against the severedvessel to provide sealing and/or coagulation of the vessel.Alternatively, a coagulation electrode located on the same or adifferent probe may be pressed against the severed vessel. Once thevessel is adequately sealed, the surgeon activates a control (e.g.,another foot pedal) to increase the voltage of the power supply backinto the ablation mode.

[0082] The present invention is particularly useful for removing orablating tissue around nerves, such as spinal or cranial nerves, e.g.,the spinal cord and the surrounding dura mater. One of the significantdrawbacks with the prior art cutters, graspers, and lasers is that thesedevices do not differentiate between the target tissue and thesurrounding nerves or bone. Therefore, the surgeon must be extremelycareful during these procedures to avoid damage to the bone or nerveswithin and around the spinal cord. In the present invention, theCoblation™ process for removing tissue results in extremely small depthsof collateral tissue damage as discussed above. This allows the surgeonto remove tissue close to a nerve without causing collateral damage tothe nerve fibers.

[0083] In addition to the generally precise nature of the novelmechanisms of the present invention, applicant has discovered anadditional method of ensuring that adjacent nerves are not damagedduring tissue removal. According to the present invention, systems andmethods are provided for distinguishing between the fatty tissueimmediately surrounding nerve fibers and the normal tissue that is to beremoved during the procedure. Nerves usually comprise a connectivetissue sheath, or endoneurium, enclosing the bundles of nerve fibers toprotect these nerve fibers. This protective tissue sheath typicallycomprises a fatty tissue (e.g., adipose tissue) having substantiallydifferent electrical properties than the normal target tissue, such asthe disc and other surrounding tissue that are, for example, removedfrom the spine during spinal procedures. The system of the presentinvention measures the electrical properties of the tissue at the tip ofthe probe with one or more electrode terminal(s). These electricalproperties may include electrical conductivity at one, several or arange of frequencies (e.g., in the range from 1 kHz to 100 MHz),dielectric constant, capacitance or combinations of these. In thisembodiment, an audible signal may be produced when the sensingelectrode(s) at the tip of the probe detects the fatty tissuesurrounding a nerve, or direct feedback control can be provided to onlysupply power to the electrode terminal(s) either individually or to thecomplete array of electrodes, if and when the tissue encountered at thetip or working end of the probe is normal tissue based on the measuredelectrical properties.

[0084] In one embodiment, the current limiting elements (discussed indetail above) are configured such that the electrode terminals will shutdown or turn off when the electrical impedance reaches a thresholdlevel. When this threshold level is set to the impedance of the fattytissue surrounding nerves, the electrode terminals will shut offwhenever they come in contact with, or in close proximity to, nerves.Meanwhile, the other electrode terminals, which are in contact with orin close proximity to nasal tissue, will continue to conduct electriccurrent to the return electrode. This selective ablation or removal oflower impedance tissue in combination with the Coblation™ mechanism ofthe present invention allows the surgeon to precisely remove tissuearound nerves or bone.

[0085] In addition to the above, applicant has discovered that theCoblation™ mechanism of the present invention can be manipulated toablate or remove certain tissue structures, while having little effecton other tissue structures. As discussed above, the present inventionuses a technique of vaporizing electrically conductive fluid to form aplasma layer or pocket around the electrode terminal(s), and theninducing the discharge of energy from this plasma or vapor layer tobreak the molecular bonds of the tissue structure. Based on initialexperiments, applicants believe that the free electrons within theionized vapor layer are accelerated in the high electric fields near theelectrode tip(s). When the density of the vapor layer (or within abubble formed in the electrically conducting liquid) becomessufficiently low (i.e., less than approximately 1020 atoms/cm3 foraqueous solutions), the electron mean free path increases to enablesubsequently injected electrons to cause impact ionization within theseregions of low density (i.e., vapor layers or bubbles). Energy evolvedby the energetic electrons (e.g., 4 to 5 eV) can subsequently bombard amolecule and break its bonds, dissociating a molecule into freeradicals, which then combine into final gaseous or liquid species.

[0086] The energy evolved by the energetic electrons may be varied byadjusting a variety of factors, such as: the number of electrodeterminals; electrode size and spacing; electrode surface area;asperities and sharp edges on the electrode surfaces; electrodematerials; applied voltage and power; current limiting means, such asinductors; electrical conductivity of the fluid in contact with theelectrodes; density of the fluid; and other factors. Accordingly, thesefactors can be manipulated to control the energy level of the excitedelectrons. Since different tissue structures have different molecularbonds, the present invention can be configured to break the molecularbonds of certain tissue, while having too low an energy to break themolecular bonds of other tissue. For example, fatty tissue, (e.g.,adipose) tissue has double bonds that require a substantially higherenergy level than 4 to 5 eV to break. Accordingly, the present inventionin its current configuration generally does not ablate or remove suchfatty tissue. Of course, factors may be changed such that these doublebonds can be broken (e.g., increasing voltage or changing the electrodeconfiguration to increase the current density at the electrode tips).

[0087] The electrosurgical probe or catheter will comprise a shaft or ahandpiece having a proximal end and a distal end which supports one ormore electrode terminal(s). The shaft or handpiece may assume a widevariety of configurations, with the primary purpose being tomechanically support the active electrode and permit the treatingphysician to manipulate the electrode from a proximal end of the shaft.The shaft may be rigid or flexible, with flexible shafts optionallybeing combined with a generally rigid external tube for mechanicalsupport. Flexible shafts may be combined with pull wires, shape memoryactuators, and other known mechanisms for effecting selective deflectionof the distal end of the shaft to facilitate positioning of theelectrode array. The shaft will usually include a plurality of wires orother conductive elements running axially therethrough to permitconnection of the electrode array to a connector at the proximal end ofthe shaft.

[0088] For endoscopic procedures within the spine, the shaft will have asuitable diameter and length to allow the surgeon to reach the targetsite (e.g., a disc) by delivering the shaft through the thoracic cavity,the abdomen or the like. Thus, the shaft will usually have a length inthe range of about 5.0 to 30.0 cm, and a diameter in the range of about0.2 mm to about 20 mm. Alternatively, the shaft may be delivereddirectly through the patient's back in a posterior approach, which wouldconsiderably reduce the required length of the shaft. In any of theseembodiments, the shaft may also be introduced through rigid or flexibleendoscopes. Specific shaft designs will be described in detail inconnection with the figures hereinafter.

[0089] In an alternative embodiment, the probe may comprise a long, thinneedle (e.g., on the order of about 1 mm in diameter or less) that canbe percutaneously introduced through the patient's back directly intothe spine (see FIGS. 34-36). The needle will include one or more activeelectrode(s) for applying electrical energy to tissues within the spine.The needle may include one or more return electrode(s), or the returnelectrode may be positioned on the patient's back, as a dispersive pad.In either embodiment, sufficient electrical energy is applied throughthe needle to the active electrode(s) to either shrink the collagenfibers within the spinal disk, or to ablate tissue within the disk.

[0090] The current flow path between the electrode terminal(s) and thereturn electrode(s) may be generated by submerging the tissue site in anelectrical conducting fluid (e.g., within a liquid or a viscous fluid,such as an electrically conductive gel) or by directing an electricallyconducting fluid along a fluid path to the target site (i.e., a liquid,such as isotonic saline, or a gas, such as argon). This latter method isparticularly effective in a dry environment (i.e., the tissue is notsubmerged in fluid) because the electrically conducting fluid provides asuitable current flow path from the electrode terminal to the returnelectrode. Finally, saline-rich tissue may be used to provide theconductive medium. A more complete description of an exemplary method ofdirecting electrically conducting fluid between the active and returnelectrodes is described in U.S. Pat. No. 5,697,536, previouslyincorporated herein by reference.

[0091] In some variations of the invention where the procedure isperformed on saline rich tissue, external conductive fluid is notrequired. For example, because the nucleus pulposus itself comprises ahighly conductive medium, delivery of a conductive fluid may not berequired. In such a case, the probe shall be advanced into the disc tothe annulus and the application of high-frequency voltage between theelectrodes may be sufficient by itself to remove the nucleus material.The fluid content of the annulus may provide the conductive mediumrequired for the ablation process described herein. In any case, asdescribed herein, the electrically conductive fluid may be a liquid orgas, such as isotonic saline, blood, extracelluar or intracellularfluid, delivered to, or already present at, the target site, or aviscous fluid, such as a gel, applied to the target site.

[0092] In some procedures, it may also be necessary to retrieve oraspirate the electrically conductive fluid after it has been directed tothe target site. In addition, it may be desirable to aspirate smallpieces of tissue that are not completely disintegrated by the highfrequency energy, or other fluids at the target site, such as blood,mucus, the gaseous products of ablation, etc. Accordingly, the system ofthe present invention will usually include a suction lumen in the probe,or on another instrument, for aspirating fluids from the target site. Inaddition, the invention may include one or more aspiration electrode(s)coupled to the distal end of the suction lumen for ablating, or at leastreducing the volume of, non-ablated tissue fragments that are aspiratedinto the lumen. The aspiration electrode(s) function mainly to inhibitclogging of the lumen that may otherwise occur as larger tissuefragments are drawn therein. The aspiration electrode(s) may bedifferent from the ablation electrode terminal(s), or the sameelectrode(s) may serve both functions. A more complete description ofprobes incorporating aspiration electrode(s) can be found in commonlyassigned, co-pending patent application entitled “SYSTEMS AND METHODSFOR TISSUE RESECTION, ABLATION AND ASPIRATION”, filed Jan. 21, 1998, thecomplete disclosure of which is incorporated herein by reference.

[0093] The present invention may use a single active electrode terminalor an electrode array distributed over a contact surface of a probe. Inthe latter embodiment, the electrode array usually includes a pluralityof independently current-limited and/or power-controlled electrodeterminals to apply electrical energy selectively to the target tissuewhile limiting the unwanted application of electrical energy to thesurrounding tissue and environment resulting from power dissipation intosurrounding electrically conductive liquids, such as blood, normalsaline, electrically conductive gel and the like. The electrodeterminals may be independently current-limited by isolating theterminals from each other and connecting each terminal to a separatepower source that is isolated from the other electrode terminals.Alternatively, the electrode terminals may be connected to each other ateither the proximal or distal ends of the probe to form a single wirethat couples to a power source.

[0094] In some embodiments, the active electrode(s) have an activeportion or surface with surface geometries shaped to promote theelectric field intensity and associated current density along theleading edges of the electrodes. Suitable surface geometries may beobtained by creating electrode shapes that include preferential sharpedges, or by creating asperities or other surface roughness on theactive surface(s) of the electrodes. Electrode shapes according to thepresent invention can include the use of formed wire (e.g., by drawinground wire through a shaping die) to form electrodes with a variety ofcross-sectional shapes, such as square, rectangular, L or V shaped, orthe like. Electrode edges may also be created by removing a portion ofthe elongate metal electrode to reshape the cross-section. For example,material can be ground along the length of a round or hollow wireelectrode to form D or C shaped wires, respectively, with edges facingin the cutting direction. Alternatively, material can be removed atclosely spaced intervals along the electrode length to form transversegrooves, slots, threads or the like along the electrodes.

[0095] Additionally or alternatively, the active electrode surface(s)may be modified through chemical, electrochemical or abrasive methods tocreate a multiplicity of surface asperities on the electrode surface.These surface asperities will promote high electric field intensitiesbetween the active electrode surface(s) and the target tissue tofacilitate ablation or cutting of the tissue. For example, surfaceasperities may be created by etching the active electrodes with etchantshaving a Ph less than 7.0 or by using a high velocity stream of abrasiveparticles (e.g., grit blasting) to create asperities on the surface ofan elongated electrode.

[0096] The active electrode(s) are typically mounted in an electricallyinsulating electrode support that extends from the electrosurgicalprobe. In some embodiments, the electrode support comprises a pluralityof wafer layers bonded together, e.g., by a glass adhesive or the like,or a single wafer. The wafer layer(s) have conductive strips printedthereon to form the electrode terminal(s) and the return electrode(s).In one embodiment, the proximal end of the wafer layer(s) will have anumber of holes extending from the conductor strips to an exposedsurface of the wafer layers for connection to electrical conductor leadtraces in the electrosurgical probe or handpiece. The wafer layerspreferably comprise a ceramic material, such as alumina, and theelectrode will preferably comprise a metallic material, such as gold,copper, platinum, palladium, tungsten, silver or the like. Suitablemultilayer ceramic electrodes are commercially available from e.g.,VisPro Corporation of Beaverton, Oreg.

[0097] In one configuration, each individual electrode terminal in theelectrode array is electrically insulated from all other electrodeterminals in the array within said probe and is connected to a powersource which is isolated from each of the other electrode terminals inthe array or to circuitry which limits or interrupts current flow to theelectrode terminal when low resistivity material (e.g., blood,electrically conductive saline irrigant or electrically conductive gel)causes a lower impedance path between the return electrode and theindividual electrode terminal. The isolated power sources for eachindividual electrode terminal may be separate power supply circuitshaving internal impedance characteristics which limit power to theassociated electrode terminal when a low impedance return path isencountered. By way of example, the isolated power source may be a userselectable constant current source. In this embodiment, lower impedancepaths will automatically result in lower resistive heating levels sincethe heating is proportional to the square of the operating current timesthe impedance. Alternatively, a single power source may be connected toeach of the electrode terminals through independently actuatableswitches, or by independent current limiting elements, such asinductors, capacitors, resistors and/or combinations thereof. Thecurrent limiting elements may be provided in the probe, connectors,cable, controller or along the conductive path from the controller tothe distal tip of the probe. Alternatively, the resistance and/orcapacitance may occur on the surface of the active electrode terminal(s)due to oxide layers which form selected electrode terminals (e.g.,titanium or a resistive coating on the surface of metal, such asplatinum).

[0098] The tip region of the probe may comprise many independentelectrode terminals designed to deliver electrical energy in thevicinity of the tip. The selective application of electrical energy tothe conductive fluid is achieved by connecting each individual electrodeterminal and the return electrode to a power source having independentlycontrolled or current limited channels. The return electrode(s) maycomprise a single tubular member of conductive material proximal to theelectrode array at the tip which also serves as a conduit for the supplyof the electrically conducting fluid between the active and returnelectrodes. Alternatively, the probe may comprise an array of returnelectrodes at the distal tip of the probe (together with the activeelectrodes) to maintain the electric current at the tip. The applicationof high frequency voltage between the return electrode(s) and theelectrode array results in the generation of high electric fieldintensities at the distal tips of the electrode terminals withconduction of high frequency current from each individual electrodeterminal to the return electrode. The current flow from each individualelectrode terminal to the return electrode(s) is controlled by eitheractive or passive means, or a combination thereof, to deliver electricalenergy to the surrounding conductive fluid while minimizing energydelivery to surrounding (non-target) tissue.

[0099] The application of a high frequency voltage between the returnelectrode(s) and the electrode terminal(s) for appropriate timeintervals effects cutting, removing, ablating, shaping, contracting orotherwise modifying the target tissue. The tissue volume over whichenergy is dissipated (i.e., a high current density exists) may beprecisely controlled, for example, by the use of a multiplicity of smallelectrode terminals whose effective diameters or principal dimensionsrange from about 5 mm to 0.01 mm, preferably from about 2 mm to 0.05 mm,and more preferably from about 1 mm to 0.1 mm. Electrode areas for bothcircular and non-circular terminals will have a contact area (perelectrode terminal) below 25 mm2, preferably being in the range from0.0001 mm2 to 1 mm2, and more preferably from 0.005 mm2 to 0.5 mm2. Thecircumscribed area of the electrode array is in the range from 0.25 mm2to 200 mm2, preferably from 0.5 mm2 to 100 mm2, and will usually includeat least two isolated electrode terminals, preferably at least fiveelectrode terminals, often greater than 10 electrode terminals and even50 or more electrode terminals, disposed over the distal contactsurfaces on the shaft. The use of small diameter electrode terminalsincreases the electric field intensity and reduces the extent or depthof tissue heating as a consequence of the divergence of current fluxlines which emanate from the exposed surface of each electrode terminal.

[0100] The area of the tissue treatment surface can vary widely, and thetissue treatment surface can assume a variety of geometries, withparticular areas and geometries being selected for specificapplications. Active electrode surfaces can have areas in the range from0.25 mm2 to 75 mm2, usually being from about 0.5 mm2 to 40 mm2. Thegeometries can be planar, concave, convex, hemispherical, conical,linear “in-line” array or virtually any other regular or irregularshape. Most commonly, the active electrode(s) or electrode terminal(s)will be formed at the distal tip of the electrosurgical probe shaft,frequently being planar, disk-shaped, or hemispherical surfaces for usein reshaping procedures or being linear arrays for use in cutting.Alternatively or additionally, the active electrode(s) may be formed onlateral surfaces of the electrosurgical probe shaft (e.g., in the mannerof a spatula), facilitating access to certain body structures inendoscopic procedures.

[0101] The electrically conducting fluid should have a thresholdconductivity to provide a suitable conductive path between the returnelectrode(s) and the electrode terminal(s). The electrical conductivityof the fluid (in units of milliSiemans per centimeter or mS/cm) willusually be greater than 0.2 mS/cm, preferably will be greater than 2mS/cm and more preferably greater than 10 mS/cm. In an exemplaryembodiment, the electrically conductive fluid is isotonic saline, whichhas a conductivity of about 17 mS/cm. Alternatively, the fluid may be anelectrically conductive gel or spray, such as a saline electrolyte gel,a conductive ECG spray, an electrode conductivity gel, an ultrasoundtransmission or scanning gel, or the like. Suitable gels or sprays arecommercially available from Graham-Field, Inc of Hauppauge, N.Y.

[0102] In some embodiments, the electrode support and the fluid outletmay be recessed from an outer surface of the probe or handpiece toconfine the electrically conductive fluid to the region immediatelysurrounding the electrode support. In addition, the shaft may be shapedso as to form a cavity around the electrode support and the fluidoutlet. This helps to assure that the electrically conductive fluid willremain in contact with the electrode terminal(s) and the returnelectrode(s) to maintain the conductive path therebetween. In addition,this will help to maintain a vapor or plasma layer between the electrodeterminal(s) and the tissue at the treatment site throughout theprocedure, which reduces the thermal damage that might otherwise occurif the vapor layer were extinguished due to a lack of conductive fluid.Provision of the electrically conductive fluid around the target sitealso helps to maintain the tissue temperature at desired levels.

[0103] The voltage applied between the return electrode(s) and theelectrode array will be at high or radio frequency, typically betweenabout 5 kHz and 20 MHz, usually being between about 30 kHz and 2.5 MHz,preferably being between about 50 kHz and 500 kHz, more preferably lessthan 350 kHz, and most preferably between about 100 kHz and 200 kHz. TheRMS (root mean square) voltage applied will usually be in the range fromabout 5 volts to 1000 volts, preferably being in the range from about 10volts to 500 volts depending on the electrode terminal size, theoperating frequency and the operation mode of the particular procedureor desired effect on the tissue (i.e., contraction, coagulation orablation). Typically, the peak-to-peak voltage will be in the range of10 to 2000 volts, preferably in the range of 20 to 1200 volts and morepreferably in the range of about 40 to 800 volts (again, depending onthe electrode size, the operating frequency and the operation mode).

[0104] As discussed above, the voltage is usually delivered in a seriesof voltage pulses or alternating current of time varying voltageamplitude with a sufficiently high frequency (e.g., on the order of 5kHz to 20 MHz) such that the voltage is effectively applied continuously(as compared with e.g., lasers claiming small depths of necrosis, whichare generally pulsed about 10 to 20 Hz). In addition, the duty cycle(i.e., cumulative time in any one-second interval that energy isapplied) is on the order of about 50% for the present invention, ascompared with pulsed lasers which typically have a duty cycle of about0.0001%.

[0105] The preferred power source of the present invention delivers ahigh frequency current selectable to generate average power levelsranging from several milliwatts to tens of watts per electrode,depending on the volume of target tissue being heated, and/or themaximum allowed temperature selected for the probe tip. The power sourceallows the user to select the voltage level according to the specificrequirements of a particular spine procedure, arthroscopic surgery,dermatological procedure, ophthalmic procedures, FESS procedure, opensurgery or other endoscopic surgery procedure. A description of asuitable power source can be found in U.S. Provisional PatentApplication No. 60/062,997 entitled “SYSTEMS AND METHODS FORELECTROSURGICAL TISSUE AND FLUID COAGULATION”, filed Oct. 23, 1997(Attorney Docket No. 16238-007400), the complete disclosure of which hasbeen incorporated herein by reference.

[0106] The power source may be current limited or otherwise controlledso that undesired heating of the target tissue or surrounding(non-target) tissue does not occur. In a presently preferred embodimentof the present invention, current limiting inductors are placed inseries with each independent electrode terminal, where the inductance ofthe inductor is in the range of 10 uH to 50,000 uH, depending on theelectrical properties of the target tissue, the desired tissue heatingrate and the operating frequency. Alternatively, capacitor-inductor (LC)circuit structures may be employed, as described previously inco-pending PCT application No. PCT/US94/05168, the complete disclosureof which is incorporated herein by reference. Additionally, currentlimiting resistors may be selected. Preferably, these resistors willhave a large positive temperature coefficient of resistance so that, asthe current level begins to rise for any individual electrode terminalin contact with a low resistance medium (e.g., saline irrigant orconductive gel), the resistance of the current limiting resistorincreases significantly, thereby minimizing the power delivery from saidelectrode terminal into the low resistance medium (e.g., saline irrigantor conductive gel).

[0107] It should be clearly understood that the invention is not limitedto electrically isolated electrode terminals, or even to a plurality ofelectrode terminals. For example, the array of active electrodeterminals may be connected to a single lead that extends through theprobe shaft to a power source of high frequency current. Alternatively,the probe may incorporate a single electrode that extends directlythrough the probe shaft or is connected to a single lead that extends tothe power source. The active electrode may have a ball shape (e.g., fortissue vaporization and desiccation), a twizzle shape (for vaporizationand needle-like cutting), a spring shape (for rapid tissue debulking anddesiccation), a twisted metal shape, an annular or solid tube shape orthe like. Alternatively, the electrode may comprise a plurality offilaments, a rigid or flexible brush electrode (for debulking a tumor,such as a lipomenengoseal), a side-effect brush electrode on a lateralsurface of the shaft, a coiled electrode or the like. In one embodiment,the probe comprises a single active electrode terminal that extends froman insulating member, e.g., ceramic, at the distal end of the probe. Theinsulating member is preferably a tubular structure that separates theactive electrode terminal from a tubular or annular return electrodepositioned proximal to the insulating member and the active electrode.

[0108] Referring to FIG. 1, an exemplary electrosurgical system 11 fortreatment of tissue in the spine will now be described in detail.Electrosurgical system 11 generally comprises an electrosurgicalhandpiece or probe 10 connected to a power supply 28 for providing highfrequency voltage to a target site and a fluid source 21 for supplyingelectrically conducting fluid 50 to probe 10. In addition,electrosurgical system 11 may include an endoscope (not shown) with afiber optic head light for viewing the surgical site, particularly inendoscopic spine procedures. The endoscope may be integral with probe10, or it may be part of a separate instrument. The system 11 may alsoinclude a vacuum source (not shown) for coupling to a suction lumen ortube 211 (see FIG. 2) in the probe 10 for aspirating the target site.

[0109] As shown, probe 10 generally includes a proximal handle 19 and anelongate shaft 18 having an array 12 of electrode terminals 58 at itsdistal end. A connecting cable 34 has a connector 26 for electricallycoupling the electrode terminals 58 to power supply 28. The electrodeterminals 58 are electrically isolated from each other and each of theterminals 58 is connected to an active or passive control network withinpower supply 28 by means of a plurality of individually insulatedconductors (not shown). A fluid supply tube 15 is connected to a fluidtube 14 of probe 10 for supplying electrically conducting fluid 50 tothe target site.

[0110] Power supply 28 has an operator controllable voltage leveladjustment 30 to change the applied voltage level, which is observableat a voltage level display 32. Power supply 28 also includes first,second and third foot pedals 37, 38, 39 and a cable 36 which isremovably coupled to power supply 28. The foot pedals 37, 38, 39 allowthe surgeon to remotely adjust the energy level applied to electrodeterminals 58. In an exemplary embodiment, first foot pedal 37 is used toplace the power supply into the “ablation” mode and second foot pedal 38places power supply 28 into the “coagulation” mode. The third foot pedal39 allows the user to adjust the voltage level within the “ablation”mode. In the ablation mode, a sufficient voltage is applied to theelectrode terminals to establish the requisite conditions for moleculardissociation of the tissue (i.e., vaporizing a portion of theelectrically conductive fluid, ionizing charged particles within thevapor layer and accelerating these charged particles against thetissue). As discussed above, the requisite voltage level for ablationwill vary depending on the number, size, shape and spacing of theelectrodes, the distance in which the electrodes extend from the supportmember, etc. Once the surgeon places the power supply in the “ablation”mode, voltage level adjustment 30 or third foot pedal 39 may be used toadjust the voltage level to adjust the degree or aggressiveness of theablation.

[0111] Of course, it will be recognized that the voltage and modality ofthe power supply may be controlled by other input devices. However,applicant has found that foot pedals are convenient methods ofcontrolling the power supply while manipulating the probe during asurgical procedure.

[0112] In the coagulation mode, the power supply 28 applies a low enoughvoltage to the electrode terminals (or the coagulation electrode) toavoid vaporization of the electrically conductive fluid and subsequentmolecular dissociation of the tissue. The surgeon may automaticallytoggle the power supply between the ablation and coagulation modes byalternatively stepping on foot pedals 37, 38, respectively. This allowsthe surgeon to quickly move between coagulation and ablation in situ,without having to remove his/her concentration from the surgical fieldor without having to request an assistant to switch the power supply. Byway of example, as the surgeon is sculpting soft tissue in the ablationmode, the probe typically will simultaneously seal and/or coagulationsmall severed vessels within the tissue. However, larger vessels, orvessels with high fluid pressures (e.g., arterial vessels) may not besealed in the ablation mode. Accordingly, the surgeon can simply step onfoot pedal 38, automatically lowering the voltage level below thethreshold level for ablation, and apply sufficient pressure onto thesevered vessel for a sufficient period of time to seal and/or coagulatethe vessel. After this is completed, the surgeon may quickly move backinto the ablation mode by stepping on foot pedal 37. A specific designof a suitable power supply for use with the present invention can befound in U.S. Provisional Patent Application No. 60/062,997, entitled“SYSTEMS AND METHODS FOR ELECTROSURGICAL TISSUE AND FLUID COAGULATION”,filed Oct. 23, 1997 (attorney docket no. 16238-007400), previouslyincorporated herein by reference.

[0113] FIGS. 2-5 illustrate an exemplary electrosurgical probe 20constructed according to the principles of the present invention. Asshown in FIG. 2, probe 20 generally includes an elongated shaft 100which may be flexible or rigid, a handle 204 coupled to the proximal endof shaft 100 and an electrode support member 102 coupled to the distalend of shaft 100. Shaft 100 preferably comprises a plastic material thatis easily molded into the shape shown in FIG. 2. In an alternativeembodiment (not shown), shaft 100 comprises an electrically conductingmaterial, usually metal, which is selected from the group comprisingtungsten, stainless steel alloys, platinum or its alloys, titanium orits alloys, molybdenum or its alloys, and nickel or its alloys. In thisembodiment, shaft 100 includes an electrically insulating jacket 108,which is typically formed as one or more electrically insulating sheathsor coatings, such as polytetrafluoroethylene, polyimide, and the like.The provision of the electrically insulating jacket over the shaftprevents direct electrical contact between these metal elements and anyadjacent body structure or the surgeon. Such direct electrical contactbetween a body structure (e.g., tendon) and an exposed electrode couldresult in unwanted heating and necrosis of the structure at the point ofcontact causing necrosis.

[0114] Handle 204 typically comprises a plastic material that is easilymolded into a suitable shape for handling by the surgeon. Handle 204defines an inner cavity (not shown) that houses the electricalconnections 250 (FIG. 5), and provides a suitable interface forconnection to an electrical connecting cable 22 (see FIG. 1). Electrodesupport member 102 extends from the distal end of shaft 100 (usuallyabout 1 to 20 mm), and provides support for a plurality of electricallyisolated electrode terminals 104 (see FIG. 4). As shown in FIG. 2, afluid tube 233 extends through an opening in handle 204, and includes aconnector 235 for connection to a fluid supply source, for supplyingelectrically conductive fluid to the target site. Fluid tube 233 iscoupled to a distal fluid tube 239 that extends along the outer surfaceof shaft 100 to an opening 237 at the distal end of the probe 20, asdiscussed in detail below. Of course, the invention is not limited tothis configuration. For example, fluid tube 233 may extend through asingle lumen (not shown) in shaft 100, or it may be coupled to aplurality of lumens (also not shown) that extend through shaft 100 to aplurality of openings at its distal end. Probe 20 may also include avalve 17 (FIG. 1) or equivalent structure for controlling the flow rateof the electrically conducting fluid to the target site.

[0115] As shown in FIGS. 3 and 4, electrode support member 102 has asubstantially planar tissue treatment surface 212 and comprises asuitable insulating material (e.g., ceramic or glass material, such asalumina, zirconia and the like) which could be formed at the time ofmanufacture in a flat, hemispherical or other shape according to therequirements of a particular procedure. The preferred support membermaterial is alumina, available from Kyocera Industrial CeramicsCorporation, Elkgrove, Ill., because of its high thermal conductivity,good electrically insulative properties, high flexural modulus,resistance to carbon tracking, biocompatibility, and high melting point.The support member 102 is adhesively joined to a tubular support member(not shown) that extends most or all of the distance between supportmember 102 and the proximal end of probe 20. The tubular memberpreferably comprises an electrically insulating material, such as anepoxy or silicone-based material.

[0116] In a preferred construction technique, electrode terminals 104extend through pre-formed openings in the support member 102 so thatthey protrude above tissue treatment surface 212 by the desireddistance. The electrodes are then bonded to the tissue treatment surface212 of support member 102, typically by an inorganic sealing material.The sealing material is selected to provide effective electricalinsulation, and good adhesion to both the alumina member 102 and theplatinum or titanium electrode terminals 104. The sealing materialadditionally should have a compatible thermal expansion coefficient anda melting point well below that of platinum or titanium and alumina orzirconia, typically being a glass or glass ceramic

[0117] In the embodiment shown in FIGS. 2-5, probe 20 includes a returnelectrode 112 for completing the current path between electrodeterminals 104 and a high frequency power supply 28 (see FIG. 1). Asshown, return electrode 112 preferably comprises an annular conductiveband coupled to the distal end of shaft 100 slightly proximal to tissuetreatment surface 212 of electrode support member 102, typically about0.5 to 10 mm and more preferably about 1 to 10 mm. Return electrode 112is coupled to a connector 258 that extends to the proximal end of probe10, where it is suitably connected to power supply 10 (FIG. 1).

[0118] As shown in FIG. 2, return electrode 112 is not directlyconnected to electrode terminals 104. To complete this current path sothat electrode terminals 104 are electrically connected to returnelectrode 112, electrically conducting fluid (e.g., isotonic saline) iscaused to flow therebetween. In the representative embodiment, theelectrically conducting fluid is delivered through an external fluidtube 239 to opening 237, as described above. Alternatively, the fluidmay be delivered by a fluid delivery element (not shown) that isseparate from probe 20. In some microendoscopic discectomy procedures,for example, the trocar cannula may be flooded with isotonic saline andthe probe 20 will be introduced into this flooded cavity. Electricallyconducting fluid will be continually resupplied with a separateinstrument to maintain the conduction path between return electrode 112and electrode terminals 104.

[0119] In alternative embodiments, the fluid path may be formed in probe20 by, for example, an inner lumen or an annular gap between the returnelectrode and a tubular support member within shaft 100 (not shown).This annular gap may be formed near the perimeter of the shaft 100 suchthat the electrically conducting fluid tends to flow radially inwardtowards the target site, or it may be formed towards the center of shaft100 so that the fluid flows radially outward. In both of theseembodiments, a fluid source (e.g., a bag of fluid elevated above thesurgical site or having a pumping device), is coupled to probe 90 via afluid supply tube (not shown) that may or may not have a controllablevalve. A more complete description of an electrosurgical probeincorporating one or more fluid lumen(s) can be found in parentapplication U.S. Pat. No. 5,697,281, filed on Jun. 7, 1995 (AttorneyDocket 16238-0006000), the complete disclosure of which has previouslybeen incorporated herein by reference.

[0120] Referring to FIG. 4, the electrically isolated electrodeterminals 104 are spaced apart over tissue treatment surface 212 ofelectrode support member 102. The tissue treatment surface andindividual electrode terminals 104 will usually have dimensions withinthe ranges set forth above. In the representative embodiment, the tissuetreatment surface 212 has a circular cross-sectional shape with adiameter in the range of about 1 mm to 30 mm, usually about 2 to 20 mm.The individual electrode terminals 104 preferably extend outward fromtissue treatment surface 212 by a distance of about 0.1 to 8 mm, usuallyabout 0.2 to 4 mm. Applicant has found that this configuration increasesthe high electric field intensities and associated current densitiesaround electrode terminals 104 to facilitate the ablation of tissue asdescribed in detail above.

[0121] In the embodiment of FIGS. 2-5, the probe includes a single,larger opening 209 in the center of tissue treatment surface 212, and aplurality of electrode terminals (e.g., about 3-15) around the perimeterof surface 212 (see FIG. 3). Alternatively, the probe may include asingle, annular, or partially annular, electrode terminal at theperimeter of the tissue treatment surface. The central opening 209 iscoupled to a suction or aspiration lumen 213 (see FIG. 2) within shaft100 and a suction tube 211 (FIG. 2) for aspirating tissue, fluids and/orgases from the target site. In this embodiment, the electricallyconductive fluid generally flows from opening 237 of fluid tube 239radially inward past electrode terminals 104 and then back through thecentral opening 209 of support member 102. Aspirating the electricallyconductive fluid during surgery allows the surgeon to see the targetsite, and it prevents the fluid from flowing into the patient's body,e.g., into the spine, the abdomen or the thoracic cavity. Thisaspiration should be controlled, however, so that the conductive fluidmaintains a conductive path between the active electrode terminal(s) andthe return electrode.

[0122] Of course, it will be recognized that the distal tip of probe mayhave a variety of different configurations. For example, the probe mayinclude a plurality of openings 209 around the outer perimeter of tissuetreatment surface 212 (this embodiment not shown in the drawings). Inthis embodiment, the electrode terminals 104 extend from the center oftissue treatment surface 212 radially inward from openings 209. Theopenings are suitably coupled to fluid tube 233 for deliveringelectrically conductive fluid to the target site, and aspiration lumen213 for aspirating the fluid after it has completed the conductive pathbetween the return electrode 112 and the electrode terminals 104.

[0123] In some embodiments, the probe 20 will also include one or moreaspiration electrode(s) coupled to the aspiration lumen for inhibitingclogging during aspiration of tissue fragments from the surgical site.As shown in FIG. 6, one or more of the active electrode terminals 104may comprise loop electrodes 140 that extend across distal opening 209of the suction lumen within shaft 100. In the representative embodiment,two of the electrode terminals 104 comprise loop electrodes 140 thatcross over the distal opening 209. Of course, it will be recognized thata variety of different configurations are possible, such as a singleloop electrode, or multiple loop electrodes having differentconfigurations than shown. In addition, the electrodes may have shapesother than loops, such as the coiled configurations shown in FIGS. 6 and7. Alternatively, the electrodes may be formed within suction lumenproximal to the distal opening 209, as shown in FIG. 8. The mainfunction of loop electrodes 140 is to ablate portions of tissue that aredrawn into the suction lumen to prevent clogging of the lumen.

[0124] Loop electrodes 140 are electrically isolated from the otherelectrode terminals 104, which can be referred to hereinafter as theablation electrodes 104. Loop electrodes 140 may or may not beelectrically isolated from each other. Loop electrodes 140 will usuallyextend only about 0.05 to 4 mm, preferably about 0.1 to 1 mm from thetissue treatment surface of electrode support member 104.

[0125] Referring now to FIGS. 7 and 8, alternative embodiments foraspiration electrodes will now be described. As shown in FIG. 7, theaspiration electrodes may comprise a pair of coiled electrodes 150 thatextend across distal opening 209 of the suction lumen. The largersurface area of the coiled electrodes 150 usually increases theeffectiveness of the electrodes 150 on tissue fragments passing throughopening 209. In FIG. 8, the aspiration electrode comprises a singlecoiled electrode 152 passing across the distal opening 209 of suctionlumen. This single electrode 152 may be sufficient to inhibit cloggingof the suction lumen. Alternatively, the aspiration electrodes may bepositioned within the suction lumen proximal to the distal opening 209.Preferably, these electrodes are close to opening 209 so that tissuedoes not clog the opening 209 before it reaches electrodes 154. In thisembodiment, a separate return electrode 156 may be provided within thesuction lumen to confine the electric currents therein.

[0126] Referring to FIG. 10, another embodiment of the present inventionincorporates an aspiration electrode 160 within the aspiration lumen 162of the probe. As shown, the electrode 160 is positioned just proximal ofdistal opening 209 so that the tissue fragments are ablated as theyenter lumen 162. In the representation embodiment, the aspirationelectrode 160 comprises a loop electrode that stretches across theaspiration lumen 162. However, it will be recognized that many otherconfigurations are possible. In this embodiment, the return electrode164 is located outside of the probe as in the previously embodiments.Alternatively, the return electrode(s) may be located within theaspiration lumen 162 with the aspiration electrode 160. For example, theinner insulating coating 163 may be exposed at portions within the lumen162 to provide a conductive path between this exposed portion of returnelectrode 164 and the aspiration electrode 160. The latter embodimenthas the advantage of confining the electric currents to within theaspiration lumen. In addition, in dry fields in which the conductivefluid is delivered to the target site, it is usually easier to maintaina conductive fluid path between the active and return electrodes in thelatter embodiment because the conductive fluid is aspirated through theaspiration lumen 162 along with the tissue fragments.

[0127] Referring to FIG. 9, another embodiment of the present inventionincorporates a wire mesh electrode 600 extending across the distalportion of aspiration lumen 162. As shown, mesh electrode 600 includes aplurality of openings 602 to allow fluids and tissue fragments to flowthrough into aspiration lumen 162. The size of the openings 602 willvary depending on a variety of factors. The mesh electrode may becoupled to the distal or proximal surfaces of ceramic support member102. Wire mesh electrode 600 comprises a conductive material, such astitanium, tantalum, steel, stainless steel, tungsten, copper, gold orthe like. In the representative embodiment, wire mesh electrode 600comprises a different material having a different electric potentialthan the active electrode terminal(s) 104. Preferably, mesh electrode600 comprises steel and electrode terminal(s) comprises tungsten.Applicant has found that a slight variance in the electrochemicalpotential of mesh electrode 600 and electrode terminal(s) 104 improvesthe performance of the device. Of course, it will be recognized that themesh electrode may be electrically insulated from active electrodeterminal(s) as in previous embodiments

[0128] Referring now to FIGS. 11A-11C, an alternative embodimentincorporating a metal screen 610 is illustrated. As shown, metal screen610 has a plurality of peripheral openings 612 for receiving electrodeterminals 104, and a plurality of inner openings 614 for allowingaspiration of fluid and tissue through opening 609 of the aspirationlumen. As shown, screen 610 is press fitted over electrode terminals 104and then adhered to shaft 100 of probe 20. Similar to the mesh electrodeembodiment, metal screen 610 may comprise a variety of conductivemetals, such as titanium, tantalum, steel, stainless steel, tungsten,copper, gold or the like. In the representative embodiment, metal screen610 is coupled directly to, or integral with, active electrodeterminal(s) 104. In this embodiment, the active electrode terminal(s)104 and the metal screen 610 are electrically coupled to each other.

[0129]FIGS. 32 and 33 illustrate alternative embodiments of the mesh andscreen aspiration electrodes. As shown in FIGS. 32A and 32B, the probemay include a conductive cage electrode 620 that extends into theaspiration lumen 162 (not shown) to increase the effect of the electrodeon aspirated tissue. FIGS. 33A-33C illustrate a dome-shaped screenelectrode 630 that includes one or more anchors 632 (four in therepresentative embodiment) for attaching the screen electrode 630 to aconductive spacer 634. Screen electrode 630 includes a plurality ofholes 631 for allowing fluid and tissue fragments to pass therethroughto aspiration lumen 162. Screen electrode 630 is sized to fit withinopening 609 of aspiration lumen 162 except for the anchors 632 whichinclude holes 633 for receiving electrode terminals 104. Spacer 634includes peripheral holes 636 for receiving electrode terminals 104 anda central hole 638 aligned with suction lumen 162. Spacer 634 mayfurther include insulated holes 640 for electrically isolating screenelectrode 630 from electrode terminals 104. As shown in FIG. 33C,dome-shaped screen electrode 630 preferably extends distally from theprobe shaft 100 about the same distance as the electrode terminals 104.Applicant has found that this configuration enhances the ablation ratefor tissue adjacent to electrode terminals 104, while still maintainingthe ability to ablate aspirated tissue fragments passing through screen630.

[0130]FIG. 5 illustrates the electrical connections 250 within handle204 for coupling electrode terminals 104 and return electrode 112 to thepower supply 28. As shown, a plurality of wires 252 extend through shaft100 to couple terminals 104 to a plurality of pins 254, which areplugged into a connector block 256 for coupling to a connecting cable 22(FIG. 1). Similarly, return electrode 112 is coupled to connector block256 via a wire 258 and a plug 260.

[0131] In some embodiments of the present invention, the probe 20further includes an identification element that is characteristic of theparticular electrode assembly so that the same power supply 28 can beused for different electrosurgical operations. In one embodiment, forexample, the probe 20 includes a voltage reduction element or a voltagereduction circuit for reducing the voltage applied between the electrodeterminals 104 and the return electrode 112. The voltage reductionelement serves to reduce the voltage applied by the power supply so thatthe voltage between the electrode terminals and the return electrode islow enough to avoid excessive power dissipation into the electricallyconducting medium and/or ablation of the soft tissue at the target site.The voltage reduction element primarily allows the electrosurgical probe20 to be compatible with other ArthroCare generators that are adapted toapply higher voltages for ablation or vaporization of tissue. Forcontraction of tissue, for example, the voltage reduction element willserve to reduce a voltage of about 100 to 135 volts rms (which is asetting of 1 on the ArthroCare Model 970 and 980 (i.e., 2000)Generators) to about 45 to 60 volts rms, which is a suitable voltage forcontraction of tissue without ablation (e.g., molecular dissociation) ofthe tissue.

[0132] Of course, for some procedures in endoscopic spine surgery, theprobe will typically not require a voltage reduction element.Alternatively, the probe may include a voltage increasing element orcircuit, if desired.

[0133] In the representative embodiment, the voltage reduction elementis a dropping capacitor 262 which has first leg 264 coupled to thereturn electrode wire 258 and a second leg 266 coupled to connectorblock 256. Of course, the capacitor may be located in other placeswithin the system, such as in, or distributed along the length of, thecable, the generator, the connector, etc. In addition, it will berecognized that other voltage reduction elements, such as diodes,transistors, inductors, resistors, capacitors or combinations thereof,may be used in conjunction with the present invention. For example, theprobe 90 may include a coded resistor (not shown) that is constructed tolower the voltage applied between return electrode 112 and electrodeterminals 104 to a suitable level for contraction of tissue. Inaddition, electrical circuits may be employed for this purpose.

[0134] Alternatively or additionally, the cable 22 that couples thepower supply 10 to the probe 90 may be used as a voltage reductionelement. The cable has an inherent capacitance that can be used toreduce the power supply voltage if the cable is placed into theelectrical circuit between the power supply, the electrode terminals andthe return electrode. In this embodiment, the cable 22 may be usedalone, or in combination with one of the voltage reduction elementsdiscussed above, e.g., a capacitor.

[0135] In some embodiments, the probe 20 will further include a switch(not shown) or other input that allows the surgeon to couple anddecouple the identification element to the rest of the electronics inthe probe 20. For example, if the surgeon would like to use the sameprobe for ablation of tissue and contraction of tissue in the sameprocedure, this can be accomplished by manipulating the switch. Thus,for ablation of tissue, the surgeon will decouple the voltage reductionelement from the electronics so that the full voltage applied by thepower source is applied to the electrodes on the probe. When the surgeondesires to reduce the voltage to a suitable level for contraction oftissue, he/she couples the voltage reduction element to the electronicsto reduce the voltage applied by the power supply to the electrodeterminals.

[0136] Further, it should be noted that the present invention can beused with a power supply that is adapted to apply a voltage within theselected range for treatment of tissue. In this embodiment, a voltagereduction element or circuitry may not be desired.

[0137] The present invention is particularly useful in microendoscopicdiscectomy procedures, e.g., for decompressing a nerve root with alumbar discectomy. As shown in FIGS. 12-15, a percutaneous penetration270 is made in the patients' back 272 so that the superior lamina 274can be accessed. Typically, a small needle (not shown) is used initiallyto localize the disc space level, and a guidewire (not shown) isinserted and advanced under lateral fluoroscopy to the inferior edge ofthe lamina 274. Sequential cannulated dilators 276 are inserted over theguide wire and each other to provide a hole from the incision 220 to thelamina 274. The first dilator may be used to “palpate” the lamina 274,assuring proper location of its tip between the spinous process andfacet complex just above the inferior edge of the lamina 274. As shownin FIG. 13, a tubular retractor 278 is then passed over the largestdilator down to the lamina 274. The dilators 276 are removed,establishing an operating corridor within the tubular retractor 278.

[0138] As shown in FIG. 13, an endoscope 280 is then inserted into thetubular retractor 278 and a ring clamp 282 is used to secure theendoscope 280. Typically, the formation of the operating corridor withinretractor 278 requires the removal of soft tissue, muscle or other typesof tissue that were forced into this corridor as the dilators 276 andretractor 278 were advanced down to the lamina 274. This tissue isusually removed with mechanical instruments, such as pituitary rongeurs,curettes, graspers, cutters, drills, microdebriders and the like.Unfortunately, these mechanical instruments greatly lengthen andincrease the complexity of the procedure. In addition, these instrumentssever blood vessels within this tissue, usually causing profuse bleedingthat obstructs the surgeon's view of the target site.

[0139] According to the present invention, an electrosurgical probe orcatheter 284 as described above is introduced into the operatingcorridor within the retractor 278 to remove the soft tissue, muscle andother obstructions from this corridor so that the surgeon can easilyaccess and visualization the lamina 274. Once the surgeon has reachedhas introduced the probe 284, electrically conductive fluid 285 isdelivered through tube 233 and opening 237 to the tissue (see FIG. 2).The fluid flows past the return electrode 112 to the electrode terminals104 at the distal end of the shaft. The rate of fluid flow is controlledwith valve 17 (FIG. 1) such that the zone between the tissue andelectrode support 102 is constantly immersed in the fluid. The powersupply 28 is then turned on and adjusted such that a high frequencyvoltage difference is applied between electrode terminals 104 and returnelectrode 112. The electrically conductive fluid provides the conductionpath (see current flux lines) between electrode terminals 104 and thereturn electrode 112.

[0140] The high frequency voltage is sufficient to convert theelectrically conductive fluid (not shown) between the target tissue andelectrode terminal(s) 104 into an ionized vapor layer or plasma (notshown). As a result of the applied voltage difference between electrodeterminal(s) 104 and the target tissue (i.e., the voltage gradient acrossthe plasma layer), charged particles in the plasma (viz., electrons) areaccelerated towards the tissue. At sufficiently high voltagedifferences, these charged particles gain sufficient energy to causedissociation of the molecular bonds within tissue structures. Thismolecular dissociation is accompanied by the volumetric removal (i.e.,ablative sublimation) of tissue and the production of low molecularweight gases, such as oxygen, nitrogen, carbon dioxide, hydrogen andmethane. The short range of the accelerated charged particles within thetissue confines the molecular dissociation process to the surface layerto minimize damage and necrosis to the underlying tissue.

[0141] During the process, the gases will be aspirated through opening209 and suction tube 211 to a vacuum source. In addition, excesselectrically conductive fluid, and other fluids (e.g., blood) will beaspirated from the operating corridor to facilitate the surgeon's view.During ablation of the tissue, the residual heat generated by thecurrent flux lines (typically less than 150° C.), will usually besufficient to coagulate any severed blood vessels at the site. If not,the surgeon may switch the power supply 28 into the coagulation mode bylowering the voltage to a level below the threshold for fluidvaporization, as discussed above. This simultaneous hemostasis resultsin less bleeding and facilitates the surgeon's ability to perform theprocedure.

[0142] Another advantage of the present invention is the ability toprecisely ablate soft tissue without causing necrosis or thermal damageto the underlying and surrounding tissues, nerves or bone. In addition,the voltage can be controlled so that the energy directed to the targetsite is insufficient to ablate the lamina 274 so that the surgeon canliterally clean the tissue off the lamina 274, without ablating orotherwise effecting significant damage to the lamina.

[0143] Referring now to FIGS. 14 and 15, once the operating corridor issufficiently cleared, a laminotomy and medial facetectomy isaccomplished either with conventional techniques (e.g., Kerrison punchor a high speed drill) or with the electrosurgical probe 284 asdiscussed above. After the nerve root is identified, medical retractioncan be achieved with a retractor 288, or the present invention can beused to ablate with precision the disc. If necessary, epidural veins arecauterized either automatically or with the coagulation mode of thepresent invention. If an annulotomy is necessary, it can be accomplishedwith a microknife or the ablation mechanism of the present inventionwhile protecting the nerve root with the retractor 288. The herniateddisc 290 is then removed with a pituitary rongeur in a standard fashion,or once again through ablation as described above.

[0144] In another embodiment, the electrosurgical probe of the presentinvention can be used to ablate and/or contract soft tissue within thedisc 290 to allow the annulus 292 to repair itself to preventreoccurrence of this procedure. For tissue contraction, a sufficientvoltage difference is applied between the electrode terminals 104 andthe return electrode 112 to elevate the tissue temperature from normalbody temperatures (e.g., 37° C.) to temperatures in the range of 45° C.to 90° C., preferably in the range from 60° C. to 70° C. Thistemperature elevation causes contraction of the collagen connectivefibers within the disc tissue so that the disc 290 withdraws into theannulus 292.

[0145] In one method of tissue contraction according to the presentinvention, an electrically conductive fluid is delivered to the targetsite as described above, and heated to a sufficient temperature toinduce contraction or shrinkage of the collagen fibers in the targettissue. The electrically conducting fluid is heated to a temperaturesufficient to substantially irreversibly contract the collagen fibers,which generally requires a tissue temperature in the range of about 45°C. to 90° C., usually about 60° C. to 70° C. The fluid is heated byapplying high frequency electrical energy to the electrode terminal(s)in contact with the electrically conducting fluid. The current emanatingfrom the electrode terminal(s) 104 heats the fluid and generates a jetor plume of heated fluid, which is directed towards the target tissue.The heated fluid elevates the temperature of the collagen sufficientlyto cause hydrothermal shrinkage of the collagen fibers. The returnelectrode 112 draws the electric current away from the tissue site tolimit the depth of penetration of the current into the tissue, therebyinhibiting molecular dissociation and breakdown of the collagen tissueand minimizing or completely avoiding damage to surrounding andunderlying tissue structures beyond the target tissue site. In anexemplary embodiment, the electrode terminal(s) 104 are held away fromthe tissue a sufficient distance such that the RF current does not passinto the tissue at all, but rather passes through the electricallyconducting fluid back to the return electrode. In this embodiment, theprimary mechanism for imparting energy to the tissue is the heatedfluid, rather than the electric current.

[0146] In an alternative embodiment, the electrode terminal(s) 104 arebrought into contact with, or close proximity to, the target tissue sothat the electric current passes directly into the tissue to a selecteddepth. In this embodiment, the return electrode draws the electriccurrent away from the tissue site to limit its depth of penetration intothe tissue. Applicant has discovered that the depth of currentpenetration also can be varied with the electrosurgical system of thepresent invention by changing the frequency of the voltage applied tothe electrode terminal and the return electrode. This is because theelectrical impedance of tissue is known to decrease with increasingfrequency due to the electrical properties of cell membranes whichsurround electrically conductive cellular fluid. At lower frequencies(e.g., less than 350 kHz), the higher tissue impedance, the presence ofthe return electrode and the electrode terminal configuration of thepresent invention (discussed in detail below) cause the current fluxlines to penetrate less deeply resulting in a smaller depth of tissueheating. In an exemplary embodiment, an operating frequency of about 100to 200 kHz is applied to the electrode terminal(s) to obtain shallowdepths of collagen shrinkage (e.g., usually less than 1.5 mm andpreferably less than 0.5 mm).

[0147] In another aspect of the invention, the size (e.g., diameter orprincipal dimension) of the electrode terminals employed for treatingthe tissue are selected according to the intended depth of tissuetreatment. As described previously in copending patent application PCTInternational Application, U.S. National Phase Serial No.PCT/US94/05168, the depth of current penetration into tissue increaseswith increasing dimensions of an individual active electrode (assumingother factors remain constant, such as the frequency of the electriccurrent, the return electrode configuration, etc.). The depth of currentpenetration (which refers to the depth at which the current density issufficient to effect a change in the tissue, such as collagen shrinkage,irreversible necrosis, etc.) is on the order of the active electrodediameter for the bipolar configuration of the present invention andoperating at a frequency of about 100 kHz to about 200 kHz. Accordingly,for applications requiring a smaller depth of current penetration, oneor more electrode terminals of smaller dimensions would be selected.Conversely, for applications requiring a greater depth of currentpenetration, one or more electrode terminals of larger dimensions wouldbe selected.

[0148] FIGS. 16-18 illustrate an alternative electrosurgical system 300specifically configured for endoscopic discectomy procedures, e.g., fortreating extruded or non-extruded herniated discs. As shown in FIG. 16system 300 includes a trocar cannula 302 for introducing a catheterassembly 304 through a percutaneous penetration in the patient to atarget disc in the patient's spine. As discussed above, the catheterassembly 304 may be introduced through the thorax in a thoracoscopicprocedure, through the abdomen in a laparascopic procedure, or directlythrough the patient's back. Catheter assembly 304 includes a catheterbody 306 with a plurality of inner lumens (not shown) and a proximal hub308 for receiving the various instruments that will pass throughcatheter body 306 to the target site. In this embodiment, assembly 304includes an electrosurgical instrument 310 with a flexible shaft 312, anaspiration catheter 314, an endoscope 316 and an illumination fibershaft 318 for viewing the target site. As shown in FIGS. 16 and 17,aspiration catheter 314 includes a distal port 320 and a proximalfitment 322 for attaching catheter 314 to a source of vacuum (notshown). Endoscope 316 will usually comprise a thin metal tube 317 with alens 324 at the distal end, and an eyepiece (not shown) at the proximalend.

[0149] In the exemplary embodiment, electrosurgical instrument 310includes a twist locking stop 330 at a proximal end of the shaft 312 forcontrolling the axial travel distance TD of the probe. As discussed indetail below, this configuration allows the surgeon to “set” thedistance of ablation within the disc. In addition, instrument 310includes a rotational indicator 334 for displaying the rotationalposition of the distal portion of instrument 310 to the surgeon. Thisrotational indicator 334 allows the surgeon to view this rotationalposition without relying on the endoscope 316 if visualization isdifficult, or if an endoscope is not being used in the procedure.

[0150] Referring now to FIG. 17, a distal portion 340 of electrosurgicalinstrument 310 and catheter body 306 will now be described. As shown,instrument 310 comprises a relatively stiff, but deflectableelectrically insulating support cannula 312 and a working end portion348 movably coupled to cannula 312 for rotational and translationalmovement of working end 348. Working end 348 of electrosurgicalinstrument 310 can be rotated and translated to ablate and remove avolume of nucleus pulposis within a disc. Support cannula 312 extendsthrough an internal lumen 344 and beyond the distal end 346 of catheterbody 306. Alternatively, support cannula 312 may be separate frominstrument 310, or even an integral part of catheter body 306. Thedistal portion of working end 348 includes an exposed return electrode350 separated from an active electrode array 352 by an insulatingsupport member 354, such as ceramic. In the representative embodiment,electrode array 352 is disposed on only one side of ceramic supportmember 354 so that its other side is insulating and thus atraumatic totissue. Instrument 310 will also include a fluid lumen (not shown)having a distal port 360 in working end 348 for delivering electricallyconductive fluid to the target site.

[0151] In use, trocar cannula 302 is introduced into a percutaneouspenetration suitable for endoscopic delivery to the target disc in thespine. A trephine (not shown) or other conventional instrument may beused to form a channel from the trocar cannula 302 through the annulusfibrosis 370 and into the nucleus pulposis. Alternatively, the probe 310may be used for this purpose, as discussed above. The working end 348 ofinstrument 310 is then advanced through cannula 302 a short distance(e.g., about 7 to 10 mm) into the nucleus pulposis 372, as shown in FIG.18. Once the electrode array 352 is in position, electrically conductivefluid is delivered through distal port 360 to immerse the activeelectrode array 352 in the fluid. The vacuum source may also beactivated to ensure a flow of conductive fluid between electrode array352 past return electrode 350 to suction port 320, if necessary. In someembodiments, the mechanical stop 330 may then be set at the proximal endof the instrument 310 to limit the axial travel distance of working end348. Preferably, this distance will be set to minimize (or completelyeliminate) ablation of the surrounding annulus.

[0152] The probe is then energized by applying a high frequency voltagebetween the electrode array 352 and return electrode 350 so thatelectric current flows through the conductive fluid from the array 352to the return electrode 350. The electric current causes vaporization ofthe fluid and ensuing molecular dissociation of the pulposus tissue asdescribed in detail above. The instrument 310 may then be translated inan axial direction forwards and backwards to the preset limits. Whilestill energized and translating, the working end 348 may also be rotatedto ablate tissue surrounding the electrode array 352. In therepresentative embodiment, working end 348 will also include aninflatable gland 380 opposite electrode array 352 to allow deflection ofworking end relative to support cannula 312. As shown in FIG. 18,working end 348 may be deflected to produce a large diameter bore withinthe pulposus, which assures close contact with tissue surfaces to beablated. Alternatively, the entire catheter body 306, or the distal endof catheter body 306 may be deflected to increase the volume of pulposusremoved.

[0153] After the desired volume of nucleus pulposis is removed (based ondirect observation through port 324, or by kinesthetic feedback frommovement of working end 348 of instrument 310), instrument 310 iswithdrawn into catheter body 306 and the catheter body is removed fromthe patient. Typically, the preferred volume of removed tissue is about0.2 to 5 cm3.

[0154] Referring to FIGS. 19-28, alternative systems and methods forablating tissue in confined (e.g., narrow) body spaces will now bedescribed. FIG. 19 illustrates an exemplary planar ablation probe 400according to the present invention. Similar to the instruments describedabove, probe 400 can be incorporated into electrosurgical system 11 (orother suitable systems) for operation in either the bipolar or monopolarmodalities. Probe 400 generally includes a support member 402, a distalworking end 404 attached to the distal end of support member 402 and aproximal handle 408 attached to the proximal end of support member 402.As shown in FIG. 19, handle 406 includes a handpiece 408 and a powersource connector 410 removably coupled to handpiece 408 for electricallyconnecting working end 404 with power supply 28 through cable 34 (seeFIG. 1).

[0155] In the embodiment shown in FIG. 19, planar ablation probe 400 isconfigured to operate in the bipolar modality. Accordingly, supportmember 402 functions as the return electrode and comprises anelectrically conducting material, such as titanium, or alloys containingone or more of nickel, chromium, iron, cobalt, copper, aluminum,platinum, molybdenum, tungsten, tantalum or carbon. In the preferredembodiment, support member 402 is an austenitic stainless steel alloy,such as stainless steel Type 304 from MicroGroup, Inc., Medway, Mass. Asshown in FIG. 19, support member 402 is substantially covered by aninsulating layer 412 to prevent electric current from damagingsurrounding tissue. An exposed portion 414 of support member 402functions as the return electrode for probe 400. Exposed portion 414 ispreferably spaced proximally from active electrodes 416 by a distance ofabout 1 to 20 mm.

[0156] Referring to FIGS. 20 and 21, planar ablation probe 400 furthercomprises a plurality of active electrodes 416 extending from anelectrically insulating spacer 418 at the distal end of support member402. Of course, it will be recognized that probe 400 may include asingle electrode depending on the size of the target tissue to betreated and the accessibility of the treatment site (see FIG. 26, forexample). Insulating spacer 418 is preferably bonded to support member402 with a suitable epoxy adhesive 419 to form a mechanical bond and afluid-tight seal. Electrodes 416 usually extend about 2.0 mm to 20 mmfrom spacer 418, and preferably less than 10 mm. A support tongue 420extends from the distal end of support member 402 to support activeelectrodes 416. Support tongue 420 and active electrodes 416 have asubstantially low profile to facilitate accessing narrow spaces withinthe patient's body, such as the spaces between adjacent vertebrae andbetween articular cartilage and the meniscus in the patient's knee.Accordingly, tongue 420 and electrodes 416 have a substantially planarprofile, usually having a combined height He of less than 4.0 mm,preferably less than 2.0 mm and more preferably less than 1.0 mm (seeFIG. 25). In the case of ablation of meniscus near articular cartilage,the height He of both the tongue 420 and electrodes 416 is preferablybetween about 0.5 to 1.5 mm. The width of electrodes 416 and supporttongue 420 will usually be less than 10.0 mm and preferably betweenabout 2.0 to 4.0 mm.

[0157] Support tongue 420 includes a “non-active” surface 422 opposingactive electrodes 416 covered with an electrically insulating layer (notshown) to minimize undesirable current flow into adjacent tissue orfluids. Non-active surface 422 is preferably atraumatic, i.e., having asmooth planar surface with rounded corners, to minimize unwanted injuryto tissue or nerves in contact therewith, such as disc tissue or thenearby spinal nerves, as the working end of probe 400 is introduced intoa narrow, confined body space. Non-active surface 422 of tongue 420 helpto minimize iatrogenic injuries to tissue and nerves so that working end404 of probe 400 can safely access confined spaces within the patient'sbody.

[0158] Referring to FIGS. 21 and 22, an electrically insulating supportmember 430 is disposed between support tongue 420 and active electrodes416 to inhibit or prevent electric current from flowing into tongue 420.Insulating member 430 and insulating layer 412 preferably comprise aceramic, glass or glass ceramic material, such as alumina. Insulatingmember 430 is mechanically bonded to support tongue 420 with a suitableepoxy adhesive to electrically insulate active electrodes 416 fromtongue 420. As shown in FIG. 26, insulating member 430 may overhangsupport tongue 420 to increase the electrical path length between theactive electrodes 416 and the insulation covered support tongue 420.

[0159] As shown in FIGS. 21-23, active electrodes 416 are preferablyconstructed from a hollow, round tube, with at least the distal portion432 of electrodes 416 being filed off to form a semi-cylindrical tubewith first and second ends 440, 442 facing away from support tongue 420.Preferably, the proximal portion 434 of electrodes 416 will remaincylindrical to facilitate the formation of a crimp-type electricalconnection between active electrodes 416 and lead wires 450 (see FIG.23). As shown in FIG. 26, cylindrical proximal portions 434 ofelectrodes 416 extend beyond spacer 418 by a slight distance of 0.1 mmto 0.4 mm. The semi-cylindrical configuration of distal electrodeportion 432 increases the electric field intensity and associatedcurrent density around the edges of ends 440, 442, as discussed above.Alternatively, active electrodes 416 may have any of the shapes andconfigurations described above or other configurations, such as squarewires, triangular shaped wires, U-shaped or channel shaped wires and thelike. In addition, the surface of active electrodes 416 may beroughened, e.g., by grit blasting, chemical or electrochemical etching,to further increase the electric field intensity and associated currentdensity around distal portions 432 of electrodes 416.

[0160] As shown in FIG. 24, each lead wire 450 terminates at a connectorpin 452 contained in a pin insulator block 454 within handpiece 408.Lead wires 450 are covered with an insulation layer (not shown), e.g.,TefzelTM, and sealed from the inner portion of support member 402 withan adhesive seal 457 (FIG. 22). In the preferred embodiment, eachelectrode 416 is coupled to a separate source of voltage within powersupply 28. To that end, connector pins 452 are removably coupled tomating receptacles 456 within connector 410 to provide electricalcommunication with active electrodes 416 and power supply 28 (FIG. 1).Electrically insulated lead wires 458 connect receptacles 456 to thecorresponding sources of voltage within power supply 28. Theelectrically conductive wall 414 of support member 402 serves as thereturn electrode, and is suitably coupled to one of the lead wires 450.

[0161] In an alternative embodiment, adjacent electrodes 416 may beconnected to the opposite polarity of source 28 so that current flowsbetween adjacent active electrodes 416 rather than between activeelectrodes 416 and return electrode 414. By way of example, FIG. 21Billustrates a distal portion of a planar ablation probe 400′ in whichelectrodes 416 a and 416 c are at one voltage polarity (i.e., positive)and electrodes 416 b and 416 d are at the opposite voltage polarity(negative). When a high frequency voltage is applied between electrodes416 a, 416 c and electrodes 416 b, 416 d in the presence of electricallyconducting liquid, current flows between electrodes 416 a, 416 c and 416b, 416 d as illustrated by current flux lines 522′. Similar to the aboveembodiments, the opposite surface 420 of working end 404′ of probe 400′is generally atraumatic and electrically insulated from activeelectrodes 416 a, 416 b, 416 c and 416 d to minimize unwanted injury totissue in contact therewith.

[0162] In an exemplary configuration, each source of voltage includes acurrent limiting element or circuitry (not shown) to provide independentcurrent limiting based on the impedance between each individualelectrode 416 and return electrode 414. The current limiting elementsmay be contained within the power supply 28, the lead wires 450, cable34, handle 406, or within portions of the support member 402 distal tohandle 406. By way of example, the current limiting elements may includeresistors, capacitors, inductors, or a combination thereof.Alternatively, the current limiting function may be performed by (1) acurrent sensing circuit which causes the interruption of current flow ifthe current flow to the electrode exceeds a predetermined value and/or(2) an impedance sensing circuit which causes the interruption ofcurrent flow (or reduces the applied voltage to zero) if the measuredimpedance is below a predetermined value. In another embodiment, two ormore of the electrodes 416 may be connected to a single lead wire 450such that all of the electrodes 416 are always at the same appliedvoltage relative to return electrode 414. Accordingly, any currentlimiting elements or circuits will modulate the current supplied or thevoltage applied to the array of electrodes 416, rather than limitingtheir current individually, as discussed in the previous embodiment.

[0163] Referring to FIGS. 25-28, methods for ablating tissue structureswith planar ablation probe 400 according to the present invention willnow be described. In particular, exemplary methods for treating adiseased meniscus within the knee (FIGS. 29-31) and for removing softtissue between adjacent vertebrae in the spine (FIG. 32) will bedescribed. In both procedures, at least the working end 404 of planarablation probe 400 is introduced to a treatment site either by minimallyinvasive techniques or open surgery. Electrically conducting liquid isdelivered to the treatment site, and voltage is applied from powersupply 28 between active electrodes 416 and return electrode 414. Thevoltage is preferably sufficient to generate electric field intensitiesnear active electrodes that form a vapor layer in the electricallyconducting liquid, and induce the discharge of energy from the vaporlayer to ablate tissue at the treatment site, as described in detailabove.

[0164] Referring to FIG. 25, working end 404 and at least the distalportion of support member 402 are introduced through a percutaneouspenetration 500, such as a cannula, into the arthroscopic cavity 502.The insertion of probe 400 is usually guided by an arthroscope (notshown) which includes a light source and a video camera to allow thesurgeon to selectively visualize a zone within the knee joint. Tomaintain a clear field of view and to facilitate the generation of avapor layer, a transparent, electrically conductive irrigant 503, suchas isotonic saline, is injected into the treatment site either through aliquid passage in support member 402 of probe 400, or through anotherinstrument. Suitable methods for delivering irrigant to a treatment siteare described in commonly assigned, co-pending application U.S. Pat. No.5,697,281 filed on Jun. 7, 1995 (Attorney Docket 16238-000600),previously incorporated herein by reference.

[0165] In the example shown in FIG. 25, the target tissue is a portionof the meniscus 506 adjacent to and in close proximity with thearticular cartilage 510, 508 which normally covers the end surfaces ofthe tibia 512 and the femur 514, respectively. The articular cartilage508, 510 is important to the normal functioning of joints, and oncedamaged, the body is generally not capable of regenerating this criticallining of the joints. Consequently, it is desirable that the surgeonexercise extreme care when treating the nearby meniscus 506 to avoidunwanted damage to the articular cartilage 508, 510. The confined spaces513 between articular cartilage 508, 510 and meniscus 506 within theknee joint are relatively narrow, typically on the order of about 1.0 mmto 5.0 mm. Accordingly, the narrow, low profile working end 404 ofablation probe 400 is ideally suited for introduction into theseconfined spaces 513 to the treatment site. As mentioned previously, thesubstantially planar arrangement of electrodes 416 and support tongue420 (typically having a combined height of about 0.5 to 1.5 mm) allowsthe surgeon to deliver working end 404 of probe 400 into the confinedspaces 513, while minimizing contact with the articular cartilage 508,510 (see FIG. 26).

[0166] As shown in FIG. 26, active electrodes 416 are disposed on oneface of working end 404 of probe 400. Accordingly, a zone 520 of highelectric field intensity is generated on each electrode 416 on one faceof working end 404 while the opposite side 521 of working end 404 isatraumatic with respect to tissue. In addition, the opposite side 521 isinsulated from electrodes 416 to minimize electric current from passingthrough this side 521 to the tissue (i.e., adjacent articular cartilage508). As shown in FIG. 26, the bipolar arrangement of active electrodes416 and return electrode 414 causes electric current to flow along fluxlines 522 predominantly through the electrically conducting irrigant503, which envelops the tissue and working end 404 of ablation probe 400and provides an electrically conducting path between electrodes 416 andreturn electrode 414. As electrodes 416 are engaged with, or positionedin close proximity to, the target meniscus 506, the high electric fieldpresent at the electrode edges cause controlled ablation of the tissueby forming a vapor layer and inducing the discharge of energy therefrom.In addition, the motion of electrodes 416 relative to the meniscus 506(as shown by vector 523) causes tissue to be removed in a controlledmanner. The presence of the irrigant also serves to minimize theincrease in the temperature of the meniscus during the ablation processbecause the irrigant generally comes in contact with the treated tissueshortly after one of the electrodes 416 has been translated across thesurface of the tissue.

[0167] Referring now to FIG. 28, an exemplary method for removing softtissue 540 from the surfaces of adjacent vertebrae 542, 544 in the spinewill now be described. Removal of this soft tissue 540 is oftennecessary, for example, in surgical procedures for fusing or joiningadjacent vertebrae together. Following the removal of tissue 540, theadjacent vertebrae 542, 544 are stabilized to allow for subsequentfusion together to form a single monolithic vertebra. As shown, thelow-profile of working end 404 of probe 400 (i.e., thickness values aslow as 0.2 mm) allows access to and surface preparation of closelyspaced vertebrae. In addition, the shaped electrodes 416 promotesubstantially high electric field intensities and associated currentdensities between active electrodes 416 and return electrode 414 toallow for the efficient removal of tissue attached to the surface ofbone without significantly damaging the underlying bone. The“non-active” insulating side 521 of working end 404 also minimizes thegeneration of electric fields on this side 521 to reduce ablation of theadjacent vertebra 542.

[0168] The target tissue is generally not completely immersed inelectrically conductive liquid during surgical procedures within thespine, such as the removal of soft tissue described above. Accordingly,electrically conducting liquid will preferably be delivered into theconfined spaces 513 between adjacent vertebrae 542, 544 during thisprocedure. The fluid may be delivered through a liquid passage (notshown) within support member 402 of probe 400, or through anothersuitable liquid supply instrument.

[0169] Other modifications and variations can be made to discloseembodiments without departing from the subject invention as defined inthe following claims. For example, it should be clearly understood thatthe planar ablation probe 400 described above may incorporate a singleactive electrode, rather than a plurality of such active electrodes asdescribed above in the exemplary embodiment. FIG. 27 illustrates aportion of a planar ablation probe according to the present inventionthat incorporates a single active electrode 416′ for generating highelectric field densities 550 to ablate a target tissue 552. Electrode416′ may extend directly from a proximal support member, as depicted inFIG. 31, or it may be supported on an underlying support tongue (notshown) as described in the previous embodiment. As shown, therepresentative single active electrode 416′ has a semi-cylindricalcross-section, similar to the electrodes 416 described above. However,the single electrode 416′ may also incorporate any of the abovedescribed configurations (e.g., square or star shaped solid wire) orother specialized configurations depending on the function of thedevice.

[0170] Referring now to FIGS. 29-31 an alternative electrode supportmember 500 for a planar ablation probe 404 will be described in detail.As shown, electrode support member 500 preferably comprises a multilayeror single layer substrate 502 comprising a suitable high temperature,electrically insulating material, such as ceramic. The substrate 502 isa thin or thick film hybrid having conductive strips that are adheredto, e.g., plated onto, the ceramic wafer. The conductive stripstypically comprise tungsten, gold, nickel or equivalent materials. Inthe exemplary embodiment, the conductive strips comprise tungsten, andthey are co-fired together with the wafer layers to form an integralpackage. The conductive strips are coupled to external wire connectorsby holes or vias that are drilled through the ceramic layers, and platedor otherwise covered with conductive material.

[0171] In the representative embodiment, support member 500 comprises asingle ceramic wafer having a plurality of longitudinal ridges 504formed on one side of the wafer 502. Typically, the wafer 502 is greenpressed and fired to form the required topography (e.g., ridges 504). Aconductive material is then adhered to the ridges 502 to form conductivestrips 506 extending axially over wafer 502 and spaced from each other.As shown in FIG. 30, the conductive strips 506 are attached to leadwires 508 within shaft 412 of the probe 404 to electrically coupleconductive strips 506 with the power supply 28 (FIG. 1). This embodimentprovides a relatively low profile working end of probe 404 that hassufficient mechanical structure to withstand bending forces during theprocedure.

[0172] FIGS. 34-36 illustrate another system and method for treatingswollen or herniated spinal discs according to the present invention. Inthis procedure, an electrosurgical probe 700 comprises a long, thinshaft 702 (e.g., on the order of about 1 mm in diameter or less) thatcan be percutaneously introduced anteriorly through the abdomen orthorax, or through the patient's back directly into the spine. The probeshaft 702 will include one or more active electrode(s) 704 for applyingelectrical energy to tissues within the spine. The probe 700 may includeone or more return electrode(s) 706, or the return electrode may bepositioned on the patient's back, as a dispersive pad (not shown).

[0173] In the embodiment shown in FIGS. 34-36, both active electrode(s)704 and return electrode 706 are disposed at the distal end of shaft702. As shown in FIG. 34, the distal portion of shaft 702 is introducedanteriorly through a small percutaneous penetration into the annulus 710of the target spinal disc. To facilitate this process, the distal end ofshaft 702 may taper down to a sharper point (e.g., a needle), which canthen be retracted to expose active electrode(s) 704. Alternatively, theelectrodes may be formed around the surface of the tapered distalportion of shaft (not shown). Irrespective of the specific configurationof the active and return electrodes, the distal end of shaft 702 isdelivered through the annulus 710 to the target nucleus pulposus 290,which may be herniated, extruded, non-extruded, or simply swollen. Asshown in FIG. 35, high frequency voltage is applied between activeelectrode(s) 704 and return electrode(s) 706 to heat the surroundingcollagen to suitable temperatures for contraction (i.e., typically about55° C. to about 70° C.). As discussed above, this procedure may beaccomplished with a monopolar configuration, as well. However, applicanthas found that the bipolar configuration shown in FIGS. 34-36 providesenhanced control of the high frequency current, which reduces the riskof spinal nerve damage.

[0174] As shown in FIGS. 35 and 36, once the nucleus pulposus 290 hasbeen sufficiently contracted to retract from impingement on the nerve720, probe 700 is removed from the target site. In the representativeembodiment, the high frequency voltage is applied between active andreturn electrode(s) 704 706 as the probe is withdrawn through theannulus 710. This voltage is sufficient to cause contraction of thecollagen fibers within the annulus 710, which allows the annulus 710 tocontract around the hole formed by probe 700, thereby improving thehealing of this hole. Thus, the probe 700 seals its own passage as it iswithdrawn from the disc. As can be seen from FIGS. 34-36, shaft 702,including the distal end portion of shaft 702 which bears electrodeterminal(s) 704 and return electrode(s) 706, remains linear duringintroduction of probe 700 into the disc (FIG. 34), while the distal endof shaft 702 is positioned within the nucleus pulposus duringapplication of the high frequency voltage (FIG. 35), and duringwithdrawal of probe 700 from the disc (FIG. 36).

[0175] Other modifications and variations can be made to discloseembodiments without departing from the subject invention as defined inthe following claims. For example, it should be noted that the inventionis not limited to an electrode array comprising a plurality of electrodeterminals. The invention could utilize a plurality of return electrodes,e.g., in a bipolar array or the like. In addition, depending on otherconditions, such as the peak-to-peak voltage, electrode diameter, etc.,a single electrode terminal may be sufficient to contract collagentissue, ablate tissue, or the like.

[0176] In addition, the active and return electrodes may both be locatedon a distal tissue treatment surface adjacent to each other. The activeand return electrodes may be located in active/return electrode pairs,or one or more return electrodes may be located on the distal tiptogether with a plurality of electrically isolated electrode terminals.The proximal return electrode may or may not be employed in theseembodiments. For example, if it is desired to maintain the current fluxlines around the distal tip of the probe, the proximal return electrodewill not be desired.

[0177] Referring now to FIG. 37, an exemplary electrosurgical system 5for contraction of collagen tissue will now be described in detail. Asshown, electrosurgical system 805 generally includes an electrosurgicalprobe 820 connected to a power supply 810 for providing high frequencyvoltage to one or more electrode terminals (not shown in FIG. 37) onprobe 820. Probe 820 includes a connector housing 844 at its proximalend, which can be removably connected to a probe receptacle 832 of aprobe cable 822. The proximal portion of cable 822 has a connector 834to couple probe 820 to power supply 810. Power supply 810 has anoperator controllable voltage level adjustment 838 to change the appliedvoltage level, which is observable at a voltage level display 840. Powersupply 810 also includes a foot pedal 824 and a cable 826 which isremovably coupled to a receptacle 830 with a cable connector 828. Thefoot pedal 824 may also include a second pedal (not shown) for remotelyadjusting the energy level applied to electrode terminals 904. Thespecific design of a power supply which may be used with theelectrosurgical probe of the present invention is described in parentapplication PCT US 94/051168, the full disclosure of which haspreviously been incorporated herein by reference.

[0178] FIGS. 38-41 illustrate an exemplary electrosurgical probe 820constructed according to the principles of the present invention. Asshown in FIG. 38, probe 820 generally includes an elongated shaft 900which may be flexible or rigid, a handle 204 coupled to the proximal endof shaft 900 and an electrode support member 902 coupled to the distalend of shaft 900. Shaft 900 preferably comprises an electricallyconducting material, usually metal, which is selected from the groupconsisting of tungsten, stainless steel alloys, platinum or its alloys,titanium or its alloys, molybdenum or its alloys, and nickel or itsalloys. Shaft 900 includes an electrically insulating jacket 908, whichis typically formed as one or more electrically insulating sheaths orcoatings, such as polytetrafluoroethylene, polyimide, and the like.Handle 804 typically comprises a plastic material that is easily moldedinto a suitable shape for handling by the surgeon. As shown in FIG. 39,handle 804 defines an inner cavity 208 that houses the electricalconnections 850 (discussed below), and provides a suitable interface forconnection to an electrical connecting cable 822 (see FIG. 37).Electrode support member 902 extends from the distal end of shaft 900(usually about 1 to 20 mm), and provides support for a plurality ofelectrically isolated electrode terminals 904 (see FIG. 41).

[0179] Referring to FIG. 41, the electrically isolated electrodeterminals 904 are spaced apart over tissue treatment surface 812 ofelectrode support member 902. The tissue treatment surface andindividual electrode terminals 904 will usually have dimensions withinthe ranges set forth above. In the representative embodiment, the tissuetreatment surface 812 has an oval cross-sectional shape with a length Lin the range of 1 mm to 20 mm and a width W in the range from 0.3 mm to7 mm. The individual electrode terminals 904 are preferablysubstantially flush with tissue treatment surface 812. Applicant hasfound that this configuration minimizes any sharp electrode edges and/orcorners that would promote excessively high electric field intensitiesand associated current densities when a high frequency voltage isapplied to the electrode terminals. It should be noted that theelectrode terminals 904 may protrude slightly outward from surface 812,typically by a distance from 0 mm to 2 mm, or the terminals may berecessed from this surface. For example, the electrode terminals 904 maybe recessed by a distance from 0.01 mm to 1 mm, preferably 0.01 mm to0.2 mm. In one embodiment of the invention, the electrode terminals areaxially adjustable relative to the tissue treatment surface so that thesurgeon can adjust the distance between the surface and the electrodeterminals.

[0180] In the embodiment shown in FIGS. 38-41, probe 20 includes areturn electrode 912 for completing the current path between electrodeterminals 904 and a high frequency power supply 810 (see FIG. 37). Asshown, return electrode 912 preferably comprises an annular exposedregion of shaft 902 slightly proximal to tissue treatment surface 812 ofelectrode support member 902, typically about 0.5 to 10 mm and morepreferably about 1 to 10 mm. Return electrode 912 is coupled to aconnector 858 that extends to the proximal end of probe 810, where it issuitably connected to power supply 810 (FIG. 37).

[0181] As shown in FIG. 38, return electrode 912 is not directlyconnected to electrode terminals 904. To complete this current path sothat electrode terminals 904 are electrically connected to returnelectrode 912, electrically conducting fluid (e.g., isotonic saline) iscaused to flow therebetween. In the representative embodiment, theelectrically conducting fluid is delivered from a fluid delivery element(not shown) that is separate from probe 820. Electrically conductingfluid will be continually resupplied to maintain the conduction pathbetween return electrode 912 and electrode terminals 904. In alternativeembodiments, the fluid path may be formed in probe 820 by, for example,an inner lumen or an annular gap (not shown) between the returnelectrode and a tubular support member within shaft 900. This annulargap may be formed near the perimeter of the shaft 900 such that theelectrically conducting fluid tends to flow radially inward towards thetarget site, or it may be formed towards the center of shaft 900 so thatthe fluid flows radially outward. In both of these embodiments, a fluidsource (e.g., a bag of fluid elevated above the surgical site or havinga pumping device), is coupled to probe 820 via a fluid supply tube (notshown) that may or may not have a controllable valve.

[0182]FIG. 40 illustrates the electrical connections 850 within handle804 for coupling electrode terminals 904 and return electrode 912 to thepower supply 10. As shown, a plurality of wires 852 extend through shaft900 to couple terminals 904 to a plurality of pins 854, which areplugged into a connector block 856 for coupling to a connecting cable 22(FIG. 1). Similarly, return electrode 912 is coupled to connector block856 via a wire 858 and a plug 860.

[0183] According to the present invention, the probe 20 further includesa voltage reduction element or a voltage reduction circuit for reducingthe voltage applied between the electrode terminals 904 and the returnelectrode 912. The voltage reduction element serves to reduce thevoltage applied by the power supply so that the voltage between theelectrode terminals and the return electrode is low enough to avoidexcessive power dissipation into the electrically conducting mediumand/or ablation of the soft tissue at the target site. The voltagereduction element primarily allows the electrosurgical probe 820 to becompatible with other ArthroCare generators that are adapted to applyhigher voltages for ablation or vaporization of tissue. Usually, thevoltage reduction element will serve to reduce a voltage of about 100 to135 volts rms (which is a setting of 1 on the ArthroCare Model 970 and980 (i.e., 2000) Generators) to about 45 to 60 volts rms, which is asuitable voltage for contraction of tissue without ablation (i.eg.,molecular dissociation) of the tissue.

[0184] In the representative embodiment, the voltage reduction elementis a dropping capacitor 862 which has first leg 864 coupled to thereturn electrode wire 858 and a second leg 866 coupled to connectorblock 856. The capacitor usually has a capacitance of about 2700 to 4000pF and preferably about 2900 to 3200 pF. Of course, the capacitor may belocated in other places within the system, such as in, or distributedalong the length of, the cable, the generator, the connector, etc. Inaddition, it will be recognized that other voltage reduction elements,such as diodes, transistors, inductors, resistors, capacitors orcombinations thereof, may be used in conjunction with the presentinvention. For example, the probe 820 may include a coded resistor (notshown) that is constructed to lower the voltage applied between returnelectrode 912 and electrode terminals 904 to a suitable level forcontraction of tissue. In addition, electrical circuits may be employedfor this purpose.

[0185] Alternatively or additionally, the cable 822 that couples thepower supply 810 to the probe 820 may be used as a voltage reductionelement. The cable has an inherent capacitance that can be used toreduce the power supply voltage if the cable is placed into theelectrical circuit between the power supply, the electrode terminals andthe return electrode. In this embodiment, the cable 822 may be usedalone, or in combination with one of the voltage reduction elementsdiscussed above, e.g., a capacitor.

[0186] Referring now to FIG. 42, the working end 842 of probe 820 isshown in contact with or in close proximity to a target tissue 920. Inparticular, electrode terminals 904 are in contact or in close proximitywith tissue 920. The volume which surrounds the working end 842 of probe820 is filled with an electrically conductive fluid 922 which may, byway of example, be isotonic saline or other biocompatible, electricallyconductive irrigant solution. When a voltage is applied between theelectrode terminals 904 and the return electrode 912, electrical currentflows between the electrode terminals 904 and the return electrode 912along current flux lines 924. The current flux lines 924 flow a shortdistance, L4, into the surface of tissue 920 and through theelectrically conductive fluid 922 in the region above the surface of thetissue to complete the electrical path between the electrode terminals924 and the return electrode 912. As a consequence of the electricalimpedance of the tissue and the proper selection of the applied voltageand current, heating of the tissue 920 occurs in a region 926 (shaded)below the surface of the tissue 920.

[0187] Another embodiment of the present invention is illustrated inFIGS. 43 and 44. This embodiment is similar previous embodiments exceptthat distal surface 936 of the electrode terminals 904 extends beyondthe plane of the distal surface 938 of the electrode support member 902by an extension length, L2. This extension length, L2, is preferably inthe range from 0.05 mm to 2 mm and more preferably is in the range from0.1 mm to 0.5 mm. All other dimensions and materials of construction aresimilar to those defined for the first embodiment described above. Asshown in FIG. 44, the distal surfaces 936 of the electrode terminals 904are in close proximity with or in direct contact with the surface oftissue 920.

[0188] The volume which surrounds the working end of probe 20 is filledwith an electrically conductive fluid 922 which may, by way of example,be isotonic saline or other biocompatible, electrically conductiveirrigant solution. When a voltage difference is applied between theelectrode terminals 904 and the return electrode 912, electrical currentflows between the electrode terminals 904 and the return electrode 912along current flux lines 924. The current flux lines 924 flow a shortdistance, L4 into the surface of tissue 920 and through the electricallyconductive fluid 922 in the region above the surface of the tissue tocomplete the electrical path between the electrode terminals 904 and thereturn electrode 912. As a consequence of the electrical impedance ofthe tissue and the proper selection of the applied voltage and current,heating of the tissue 920 occurs in a region 926 below the surface ofthe tissue 920, said heating elevating the temperature of the tissuefrom normal body temperature (e.g. 37° C.) to a temperature in the range55° C. to 85° C., preferably in the range from 60° C. to 70° C.

[0189] Referring now to FIG. 45, an alternative method of contractingcollagen soft tissue according to the present invention will now bedescribed. As shown, one or more electrode terminals 904 on the distalend of an electrosurgical instrument 900 are positioned adjacent to thetarget tissue 920. In this method, electrically conducting fluid isdelivered to the target site to submerge the target tissue 920 and thedistal portion of instrument 900 in the fluid. As discussed above, thefluid may be delivered through instrument 900, or by a separate deliveryinstrument. When a voltage difference is applied between the electrodeterminals 904 and the return electrode 912, electrical current flowsbetween the electrode terminals 904 and the return electrode 912 throughthe conductive fluid, as shown by current flux lines 924. The currentflux lines 924 heat the electrically conductive fluid. Since theelectrode terminals are spaced from the tissue 920 (preferably about 0.5to 10 mm), the current flux lines 924 flow only in the electricallyconductive fluid such that little or no current flows in the adjacenttissue 920. By virtue of the current flow through the electricallyconductive fluid 922 in the region above the surface of the tissue,heated fluid is caused to flow away from the working end 842 towards thetarget tissue 920 along heated fluid path 928. Alternatively, the fluidmay be delivered past the electrode terminals 904 in a jet of fluid thatis delivered onto the target tissue to effect a more define zone ofheating. The heated fluid elevates the temperature of the tissue fromnormal body temperatures (e.g., 37° C.) to temperatures in the rangefrom 55° C. to 85° C., preferably in the range from 60° C. to 70° C.

[0190] Still yet another embodiment of the present invention isillustrated in FIG. 46. This embodiment is similar to previousembodiments except that the electrode terminals 904 are joined to asingle electrode terminal lead 940 through a low resistance bond 914. Byway of example, low resistance bond 914 may be effective through the useof solder, braze, weld, electrically conductive adhesive, and/orcrimping active electrode wires 904 within a deformable metal sleeve(not shown). In the configuration shown in FIG. 46, all active electrodeleads are maintained at the same potential independent of the currentflowing between a particular electrode terminal 904 and the returnelectrode. This configuration offers the simplicity of requiring onlytwo leads between the generator 810 and the working end 842 of probe820, viz., one lead for the electrode terminals 904 and one lead for thereturn electrode.

[0191] Still yet another embodiment of the present invention isillustrated in FIGS. 47 and 48. In this embodiment, a singletubular-shaped electrode 904 replaces the array of electrode terminals.Other than the configuration and number of electrode terminal(s), allother dimensions and materials of construction remain the same as thosedescribed herein above for the first embodiment. The tubular electrodeterminal 904 may conventionally be constructed using metal tubing formedby conventional tube drawing (e.g., welded and drawn or seamless drawn)processes. The inside diameter, D3 of the tubular electrode ispreferably in the range from 0.3 mm to 5 mm and the thickness of thetubing, W4 is preferably in the range from 0.05 mm to 1 mm and morepreferably in the range from 0.1 mm to 0.6 mm.

[0192] The distance between the outer perimeter of the electrodeterminals 904 and the perimeter of the electrode support member, W3 ispreferably in the range from 0.1 mm to 1.5 mm and more preferably in therange from 0.2 mm to 0.75 mm. As discussed above with respect to FIG.46, this embodiment provides the advantage of requiring only one leadbetween the electrode terminal 904 at the working end 42 of probe 20 andthe generator 10. As before, current flows between electrode terminal904 and return electrode 912 through the adjacent target tissue 920 andthe intervening electrically conductive fluid in the manner describedabove.

[0193] Yet another embodiment of the present invention is illustrated inFIGS. 49 and 50. This embodiment is similar to previous embodimentsexcept that a supply channel for the electrically conductive fluid isprovided to allow the working end 842 of probe 820 to be used inapplications where the volume surrounding the working end 842 of theprobe 820 and tissue 920 is not filled with an electrically conductiveliquid (e.g., an irrigant fluid compartment surrounding the knee orshoulder joint). As a consequence, the embodiment shown in FIG. 49 canbe used on tissue surfaces that are otherwise dry (e.g., the surface ofthe skin).

[0194] As shown in FIGS. 49 and 50, electrically conductive fluid 922 issupplied through an annular space formed between cannula 918 and outersleeve 916. Outer sleeve 916 may be an electrically insulating material(e.g., polyimide or polyethylene tubing), or a metallic tubular membercovered by an electrically insulating sleeve 908 as described above. Theelectrically conductive fluid is caused to move along flow path 932 andexit the annular flow space at annular orifice 934. As shown in FIG. 49,the application of a voltage difference between the electrode terminalor electrodes 904 and the return electrode 912 causes current flowthrough the tissue 920 in region 926 and along the stream ofelectrically conductive fluid 922 to complete the electrical circuit.All other dimensions and materials of construction are the same asdefined for the preceding embodiments.

[0195] FIGS. 51-53 show an additional variation of the inventive methodfor use with a vertebral disc 701 that has an existing fissure oropening 702 in the annulus 710. It is contemplated that the fissure 711may be the result of an earlier procedure performed to remove a portionof the disc that impinged on the spinal nerves or nerve roots. (e.g.,The fissure results from a previous entryway into the nucleus of thedisc caused by a procedure to debulk the disc as discussed above)Alternatively, the fissure may be the result of disc degeneration inwhich there is an increased risk that a portion of disc nucleus wouldextrude form the fissure in the annulus and impinge on the spinal canal.In any case, prior to the invention discussed herein, it was standardfor surgeons to commonly remove an excessive amount of nucleus materialfrom the disc to reduce the potential of herniations of the nucleusthrough the annulus.

[0196] It should be noted that the inventive method is not limited toany particular means of accessing the disc. For example, the probe mayaccess the spinal column and disc either anteriorly or posteriorly.Furthermore, the procedure may be performed in either an open surgicalprocedure or in a minimally invasive procedure. For sake of convenience,the illustrations show the probe 700 accessing the disc in aposterior-type approach.

[0197]FIG. 52 illustrates a treatment device 700 advanced into the disc701 to apply heat to the nucleus pulposus 290 in an area 703 adjacent toa site where a potential herniation or re-herniation may occur. Asdiscussed herein, shrinkage of the respective area 703 of nucleuspulposus may be accomplished using RF energy to establish electricalcurrent flow through the tissue of interest, and/or indirectly throughthe exposure of the tissue to fluid heated by RF energy. In either case,the temperature of the tissue is increased from normal body temperatures(e.g., 37° C.) to temperatures in the range of 45° C. to 90° C.,preferably in the range from about 60° C. to 70° C.

[0198] The heating of the nucleus contracts the nucleus, transforming itfrom the loose or amorphous structure described above to a morecontracted and stable structure. The heating of the nucleus forms anarea that is “sealed” and prevents the remaining amorphous nucleusmaterial from migrating out through the annulus. Thus, the treatmentlowers the probability of a herniation or a re-herniation.

[0199] As shown in FIG. 52, the treatment device 700 may be advancedinto the disc through an opening 705 that is separate from the fissure711. However, since it is important to preserve the integrity of theannulus 710 to prevent further deterioration of the disc, advancement ofthe device 700 may be performed to minimize the damage to the annulus.Commonly assigned U.S. Provisional Application No. 60/408,967 filed Sep.5, 2002 entitled “METHODS AND APPARATUS FOR TREATING INTERVERTEBRALDISCS”, the entirety of which is incorporated by reference herein,discusses methods and devices for entering the disc through the annulusto minimize resulting damage. Such methods and devices may be combinedwith the present invention to perform a less traumatic procedure on thedisc.

[0200] Alternatively, although not shown, the device 700 may enter thedisc through the pre-existing opening 711. Accordingly, the device 700will be easily able to coagulate the nucleus pulposus 290 adjacent tothe fissure 711.

[0201] As discussed in more detail above, the probe for use with theinventive method may comprise a plurality of electrodes that are coupledto a high frequency power supply. The plurality of electrodes comprisesat least one active electrode, and at least one return electrode 706.The probe may have one or more active electrodes. Additional probessuitable for use with the invention are disclosed in commonly assignedU.S. patent applications and patent Nos.: Ser. No. 09/571,343, filed May16, 2000; Ser. No. 10/374,411, filed Feb. 25, 2003; U.S. Pat. Nos.6,179,836; and 6,468,274 the entirety of each of which is incorporatedby reference herein.

[0202] The method of treating the nucleus pulposus to minimize/preventherniation or reherniations of the disc may be combined with the act ofablation and/or vaporizing portions of the nucleus pulposus to debulkthe nucleus for treatment of herniations (described above.) In suchcases, the treatment device 700 may operate in an ablative/vaporizationmode to ablate portions of the nucleus pulposus. After a sufficientamount of the nucleus is debulked, the treatment device may operate in acoagulation or heating mode to shrink portions of the nucleus (see FIG.52) that are at greater risk of extruding through the annulus.

[0203] It is also contemplated that the acts of ablating the nucleus andcontracting the nucleus may be performed with separate devices. Thedevice used to ablate the nucleus would be configured to generate theplasma layer, as discussed above. While the device used to contract orcoagulate the portion of the nucleus at risk of extruding through theannulus would be configured as an electrode. The benefit of havingseparate devices is that the coagulation/heating device may be able toconfigured to have a larger electrode surface that is conducive tocontracting large portions of the nucleus. The coagulation device wouldnot be required to generate the plasma layer required to ablate tissue.

[0204]FIG. 53 illustrates yet another variation of the inventive method.In this case, after sealing of the respective portion of the nucleusthat may be at risk for extruding through the annulus, an implantmaterial and/or sealant 291 may be inserted into the disc to furtherimprove stability of the disc. As shown, the implant material/sealant291 may be placed between the contracted portion of the nucleus pulposusand the fissure. Possible examples of sealant/implant materials includea polyurethane, hydrogel, protein hydrogel, or thermopolymer, adhesive,collagen, or figrogen glue. Alternatively, or in combination, theimplant may comprise a ceramic or metal implant such as those that arecommonly known.

What is claimed is:
 1. A method for inhibiting herniation and/orreherniation of a vertebral disc, the vertebral disc including anannulus, a nucleus pulposus, and at least one fissure in the annulus,the method comprising: positioning a distal end of a shaft of anelectrosurgical probe into the disc, the probe having a plurality ofelectrodes coupled to a high frequency power supply, the plurality ofelectrodes comprising at least one active electrode and at least onereturn electrode, the active electrode being disposed towards the distalend of the shaft; positioning the at least one active electrode within aportion of the nucleus pulposus, the portion being adjacent to and/or incontact with the fissure; and contracting the portion of nucleuspulposus by applying a high frequency voltage between the at least oneactive electrode and the at least one return electrode within theportion of the nucleus pulposus, where contraction of the portion ofnucleus pulposus inhibits migration of the portion nucleus pulposusthrough the fissure.
 2. The method of claim 1, further comprisingablating or vaporizing the nucleus pulposus.
 3. The method of claim 2,wherein ablating or vaporizing the nucleus pulposus occurs prior to theact of contracting the portion of nucleus pulposus.
 4. The method ofclaim 2, wherein ablating or vaporizing nucleus pulposus occurssubsequent or contemporaneous to the act of contracting the portion ofnucleus pulposus.
 5. The method of claim 2, wherein the electrosurgicalprobe is a first electrosurgical probe, and a second electrosurgicalprobe is used for ablating or vaporizing the nucleus pulposus, where thefirst electrosurgical probe is not adapted to ablate and/or vaporize. 6.The method of claim 2, wherein the act of ablating or vaporizing nucleuspulposus of the disc further comprises placing an electricallyconductive medium in contact with the active and return electrodes. 7.The method of claim 6, wherein ablating or vaporizing nucleus pulposuscomprises generating electric field intensities between the at least oneactive electrode and at least one return electrode such that theelectric field intensities are sufficient to vaporize at least a portionof the conductive medium in contact with one of the active electrodes.8. The method of claim 6, where placing an electrically conductivemedium comprises providing an electrically conductive fluid into thedisc.
 9. The method of claim 6, where placing an electrically conductivemedium comprises providing an electrically conductive gel onto thedistal end of a shaft.
 10. The method of claim 6, where the conductivemedium comprises saline rich tissue of the disc.
 11. The method of claim6 further comprising aspirating at least a portion of the conductingmedium.
 12. The method of claim 1, further comprising inserting animplant material into the disc.
 13. The method of claim 11, where theimplant material comprises a material selected from the group consistingof a metal, ceramic, polyurethane, hydrogel, protein hydrogel,thermopolymer, adhesive, collagen, and fibrogen glue.
 14. The method ofclaim 12, wherein inserting the implant material comprises inserting theimplant material between the contracted portion of the nucleus pulposusand the fissure.
 15. The method of claim 1, further comprising insertinga sealant into the disc.
 16. The method of claim 15, wherein the sealantis selected from a group consisting of an adhesive, collagen, andfibrogen glue.
 17. The method of claim 1, wherein electrosurgical probecomprises a tissue treatment portion which contains at least the activeelectrodes.
 18. The method of claim 17, where the tissue treatmentsurface is curved and adapted to treat the interior of the disc.
 19. Themethod of claim 17, where the tissue treatment surface has an axiallength and a thickness substantially less than the axial length and awidth substantially larger than said thickness to form a substantiallyplanar body having an active side and a non-active side opposing theactive side, wherein at least the active electrodes are on the activeside.
 20. The method of claim 1, where the shaft is curved.
 21. Themethod of claim 1, wherein the at least one return electrode is locatedtowards a distal end of the shaft.
 22. The method of claim 1, whereinthe at least one return electrode is located on the outer surface of thepatient's body.
 23. The method of claim 1, wherein the at least oneactive electrode comprises a single, active electrode at the distal endof a shaft.
 24. The method of claim 1, wherein the at least one activeelectrode comprises a plurality of electrically isolated activeelectrodes at the distal end of a shaft.
 25. The method of claim 2further comprising aspirating at least a portion of the conductingfluid.
 26. The method of claim 1, further comprising independentlycontrolling current flow from the at least one active electrode based onimpedance between the electrodes.
 27. The method of claim 1, wherein theat least one return electrode is axially spaced on the shaft from the atleast active electrode.
 28. The method of claim 1, wherein thepositioning step comprises introducing at least a distal portion of theelectrosurgical probe through a percutaneous penetration in a patient.29. The method of claim 28, wherein the percutaneous penetration islocated on the patient's back, abdomen, or thorax.
 30. The method ofclaim 1, wherein the positioning step comprises introducing at least adistal portion of the electrosurgical probe anteriorly through thepatient to the spine.
 31. The method of claim 1, wherein the act ofpositioning comprises advancing the distal end of the shaft through anexisting opening in the annulus fibrosus.
 32. The method of claim 31,wherein the existing opening comprises the fissure in the annulus. 33.The method of claim 1, wherein the act of positioning comprisesadvancing the distal end of the shaft through a wall of the annulusfibrosus.
 34. The method of claim 1, wherein the contracting act causesthe portion of nucleus pulposus to be heated to a temperature in therange of from about 45° C. to 90° C.
 35. The method of claim 34, whereinthe contracting act causes the portion of nucleus pulposus to be heatedto a temperature in the range of from about 60° C. to 70° C.